Limiting Factors For Takeoff [Archive]

AeroTech

25th May 2010, 17:31

Hi,

Thank you for your posts.
I don’t have any specific aircraft or runway in my mind. I just wanted to have a general idea about takeoff limitations for airliners in the majority of runways. But it seems there is no single answer to my question.

And if you really want an interesting one, look at a MD11 from a hot/high airport and you will find that it is limited by its ability to dump fuel .

Mutt, it will be nice if you can give more details.

I am wondering if takeoff thrust time limit is limiting factor on takeoff.

Let say an engine fails on takeoff and for some reason (missed approach) the pilot makes a go-around during air turn-back to the departure airport. Using takeoff thrust twice in such period of time may affect the reliability of the engine especially that most of engine failures occur at high thrust.
In such situation can pilot disregard the go-around and land as soon as possible, or perform the around and land? I am assuming the engine failure doesn’t affect the safety of aircraft like engine fire.

It is much less interesting considering the fact that the OP posted 2 similar questions then disappeared.

When someone posts a question like that, then does not participate in the ensuing discussion, I consider the person a troll and not worthy of future responses. I can understand a newbie or 3 coming on with a question AND a lack of knowledge of the SEARCH function, but those are relatively rare. This particular OP has supposedly been here for 5 years, so he knows better...

It’s true that internet made the world small town, but still members on this forum live all over the world. While I am sleeping in the States other member in the other part of the world is working. I assume many active members in this forum (Tech Log) are pilots: they might be out of town, out the country, or even in other continent. Other people are busy and they have their own schedule to check this forum. So I gave them time to answer and also sometimes it takes time to understand something that I didn’t understand, or ask the next question, or ….

It seems you want to intrude your own rules in this forum, but fortunately there is a moderator here. I am grateful to all members for their responses and also for their previous posts when I use “search function). I am grateful to you “Intruder” if you post useful and technical posts regarding the subject of my post. But if you don’t like my posts or you are “allergic” to my posts just disregard them.

Thank you and feedback appreciated
Regards

johns7022

25th May 2010, 19:48

If the OP is gone, and the heavy hitters are here......maybe this thread can move off of the kid stuff...and discuss the logic of reduced thrust departures a little bit.

galaxy flyer

25th May 2010, 20:00

And there is a problem with reduced thrust take-offs?

GF

aterpster

25th May 2010, 21:47

Johns7022:
If the OP is gone, and the heavy hitters are here......maybe this thread can move off of the kid stuff...and discuss the logic of reduced thrust departures a little bit.

The primary logic is to extend engine life substantially with no decrease in safety provided they are done correctly.

FE Hoppy

25th May 2010, 21:55

discuss the logic of reduced thrust departures a little bit.

When I have more space available than I need at full thrust I can reduce the thrust to the point that the space I need equals the space available.

aterpster

25th May 2010, 23:55

FE Hoppy:
When I have more space available than I need at full thrust I can reduce the thrust to the point that the space I need equals the space available.

That's the balanced runway part. The reduced thrust also needs to meet, or exceed the Part 25 takeoff path unless an engine fails after V1 in which case you then need to advance the good engine(s) to max takeoff thrust.

FE Hoppy

26th May 2010, 00:57

you then need to advance the good engine(s) to max takeoff thrust.

Hmm. now we really are getting into interesting territory. I know a little jet with an ATTCS that will do that for me and I'm not allowed to go if it's inop. I also know quite a few big jets where my performance after Vef is predicated on the assumed temperature thrust and I need not advance the thrust levers.
I also know a jet where advancing the thrust lever on the good engine could well cause me to loose shall we say "control on the ground".

If we swap my "space" for the more commonly used " performance" then I think it covers the whole concept quite nicely.

Oh yes, I detest "balanced fields" and never use them.

aterpster

26th May 2010, 01:19

FE Hoppy:
Hmm. now we really are getting into interesting territory. I know a little jet with an ATTCS that will do that for me and I'm not allowed to go if it's inop. I also know quite a few big jets where my performance after Vef is predicated on the assumed temperature thrust and I need not advance the thrust levers.

No doubt that almost any lightly loaded transport jet could perform the profile with reduced thrust after an engine failure. But, that is simply not the categorical case. (weight, performance, etc.)

I also know a jet where advancing the thrust lever on the good engine could well cause me to loose shall we say "control on the ground".

No doubt, if below takeoff power VMCg. But, no competent performance engineer would permit that to happen.

If we swap my "space" for the more commonly used " performance" then I think it covers the whole concept quite nicely.

I don't understand what you are saying.

Oh yes, I detest "balanced fields" and never use them.

That is not an option for commercial operations in the U.S. It's "nice" that you as an individual get to make that determination.

john_tullamarine

26th May 2010, 01:38

When I have more space available than I need at full thrust I can reduce the thrust to the point that the space I need equals the space available.

Qantas was one of the leading lights in the reduced thrust development process. Wal Stack, at the time the boss ops engineer (and a thoroughly nice bloke as well as having a flying history), took the view that he would leave around a 1000ft accel stop pad for his crews, mum and the kids. I still think that that was a good strategy rather than going to the limiting case for the sake of a few extra kilos.

That's the balanced runway part.

Confusing two concepts I fear.

in which case you then need to advance the good engine(s) to max takeoff thrust.

Never the case. While the pilot retains the ability to advance thrust up to the relevant rating, reduced thrust is based on the philosophy that there is no need or requirement to do so. The caveat is that, should the pilot chose to advance the throttles, he/she should do so SLOWLY.

I also know a jet where advancing the thrust lever on the good engine could well cause me to loose shall we say "control on the ground".

Not only a problem with jets. I was involved in the investigation of a turboprop fatal in which our conclusion was that the pilots pushed up the throttles with an overshoot leading to a Vmca departure and the ensuing fireball ....

But, that is simply not the categorical case. (weight, performance, etc.)

Time for you to produce evidence to support such a statement ?

But, no competent performance engineer would permit that to happen

Said competent performance engineer is presuming that the pilot is NOT going to push up the throttles ...

Balanced Field Length

.. should always be optional other than for those aircraft which only have BFL AFM data (DC9 for instance, as I recall)

de facto

26th May 2010, 03:53

John tullamarine,

You are correct my post #3 was written too quickly,I meant Vmca will INCREASE and your actual aircraft speed will be below Vmca.

....But, no competent performance engineer would permit that to happen

Said competent performance engineer is presuming that the pilot is NOT going to push up the throttles ...

Nicely put...
If i misspell your name,apologies Im again on the run:sad:

johns7022

26th May 2010, 06:05

aterpster

26th May 2010, 09:23

de facto:
....But, no competent performance engineer would permit that to happen

Said competent performance engineer is presuming that the pilot is NOT going to push up the throttles ...

If the aircraft is at V2 (or slightly greater) Vmca is not a factor with an engine failure. If the takeoff flight path is obstacle limited then not increasing the power after an engine failure will limit payload, or perhaps cause the takeoff flight path to fall below minimum regulatory requirements. V1 must be above Vmcg and V2 must be above Vmca, otherwise the takeoff flight performance calculations are bogus.

mutt

26th May 2010, 12:00

And if you really want an interesting one, look at a MD11 from a hot/high airport and you will find that it is limited by its ability to dump fuel . Actually it applies to ALL FAR 25 aircraft as it is determined by FAR25.1001 (IIRC) The aircraft must be able to meet approach/landing climb criteria 15 minutes after takeoff with or without a fuel dumping system. The MD11 AFM actually has a section detailing the weights associated with this limitation.

But, that is simply not the categorical case. (weight, performance, etc.) Sorry but you are incorrect, we operate a WIDE range of aircraft, most are permitted to use DERATE/ASSUMED/FLEX thrust, ONLY ONE OF THEM is required to advance the throttle following an engine failure, and that is the aircraft that FE Hoppy is talking about.

That is not an option for commercial operations in the U.S We operate under FAR91/121/135, we operate some aircraft with BALANCED FIELD, some without.

It's "nice" that you as an individual get to make that determination. Believe it or not, I was able to make that determination :):) Based upon the aircraft's capabilities and payload advantages.

might rethink this is I pull up right at the fence(because I calculated balanced field into the overrun).. Most of our corporate fleet that has the option of DERATE/ASSUMED/FLEX thrust use it. It increases the blade life on some of our engines by 12%, which translates into a financial saving, much to the bosses pleasure.

Aero tech, some of our aircraft are limited to 5 minutes takeoff thrust, some to 10 minutes, some to 5 minutes but 10 minutes in the event of an engine failure. And yes you were right, some of us are on the road hiding out in strange hotels :)

Mutt

john_tullamarine

26th May 2010, 13:33

aterpster -

If the aircraft is at V2 (or slightly greater) Vmca is not a factor with an engine failure

If the speed schedule is V2min limited (generally at minimum weight, say a short ferry flight), then Vmca might not be too far below V2. Mishandle the failure by banking the wrong way and it might get interesting - depends on CG etc on the day but not something to be dismissed as you appear to be doing I suggest.

If the takeoff flight path is obstacle limited then not increasing the power after an engine failure will limit payload

In general that is not so as the reduced thrust takeoff has already considered the obstacle profile (and all the usual things which go into determining the RTOW).

Also, if you have commenced the takeoff, which appears to be a prerequisite to having an engine failure consideration, then how can pushing up the throttle increase your payload at the time you have the failure during the takeoff ? .. or am I missing something obvious to you but mystifying to me ?

perhaps cause the takeoff flight path to fall below minimum regulatory requirements

Likewise, not so as ALL the regulatory requirements have been considered in determining the reduced thrust RTOW data.

I think that we need to call your bluff and ask you to cite some authoritative data to support your claims ?

Now, mutt and I are experienced ops engineers and I don't think we have knowledge of such generic problems ....

aterpster

26th May 2010, 13:38

Mutt:
We operate under FAR91/121/135, we operate some aircraft with BALANCED FIELD, some without.

So how do you avoid 91.605, 121.189, or 135.379?

aterpster

26th May 2010, 14:11

john tullamarine:
I think that we need to call your bluff and ask you to cite some authoritative data to support your claims ?

Now, mutt and I are experienced ops engineers and I don't think we have knowledge of such generic problems ....

I am not a performance engineer, I am a TERPs sort of guy. When I used to be a real pilot (TWA) required us to increase power on the remaining engine (s) in the event of an engine failure after achieving V2 speed.

They also taught at the school house that payload was predicated on reduced thrust with all engines operating and with takeoff power in the event of an engine failure.

Wouldn't be the first time they taught bum scoop.

Having said that, at an airport where obstacles limit the flight path, I would be on a fool's errand if I did not increase thrust on the remaining engine (s) rather than hope to clear that ridgeline 7 miles away by 35 feet. :rolleyes:

TWA also did not assess more than 300 feet each side of the takeoff flight path (beyond the airport boundary), which was another reason for advancing to takeoff power in the event of an engine failure.

Denti

26th May 2010, 14:49

Increasing power on the remaining seems like good sense. Until you have to deal with fixed derates and the associated effects. Are you sure your full thrust Vmca is below your fully derated V2? If not you certainly will live (very short) in interesting times after advancing the remaining engine to full thrust. Boeing advised us that using the Boeing performance calculation tool we should not advance any thrust levers until we go to MCT if using fixed derates, which we do nearly every single take off (combined with assumed temperature of course).

aterpster

26th May 2010, 16:47

Denti:

Increasing power on the remaining seems like good sense. Until you have to deal with fixed derates and the associated effects. Are you sure your full thrust Vmca is below your fully derated V2? If not you certainly will live (very short) in interesting times after advancing the remaining engine to full thrust. Boeing advised us that using the Boeing performance calculation tool we should not advance any thrust levers until we go to MCT if using fixed derates, which we do nearly every single take off (combined with assumed temperature of course).

When I did this we changed V1 for derated thrust, but V2 was never changed.

Denti

26th May 2010, 17:22

Well, that explains that. Today we play around with all parameters, including V2 which can vary by as much as 40kts for the same conditions depending what you allow the program to calculate.

aterpster

26th May 2010, 18:41

Denti:
Well, that explains that. Today we play around with all parameters, including V2 which can vary by as much as 40kts for the same conditions depending what you allow the program to calculate.

V2 varied greatly by weight, but not by power setting.

aterpster

26th May 2010, 18:48

john tullamarine:
f the speed schedule is V2min limited (generally at minimum weight, say a short ferry flight), then Vmca might not be too far below V2. Mishandle the failure by banking the wrong way and it might get interesting - depends on CG etc on the day but not something to be dismissed as you appear to be doing I suggest.

On a light weight, say ferry flight, deck angle would be limiting, thus we accepted a speed well over V2. But, we knew when V2 was Vmca limited, so with a light weight engine failure say at rotation, common sense said to accept a speed greater than V2 and deck angle limits may have still come into play. We never practiced those, however.

Denti

26th May 2010, 18:56

Did you use improved climb V2s? With software, but even without it, all speeds are very flexible within the given parameters. Without software you are just limited to the amount of documentation you want to carry along which nearly allways leads to simplification and fixed parameters simply to reduce the paper- and workload.

mutt

26th May 2010, 22:01

So how do you avoid 91.605, 121.189, or 135.379? We don't avoid the regulations:

§ 91.605 Transport category civil airplane weight limitations.

(4) Where the takeoff distance includes a clearway, the clearway distance is not greater than one-half of—

(i) The takeoff run, in the case of airplanes certificated after September 30, 1958, and before August 30, 1959; or

(ii) The runway length, in the case of airplanes certificated after August 29, 1959.

(c) No person may take off a turbine-engine-powered transport category airplane certificated after August 29, 1959, unless, in addition to the requirements of paragraph (b) of this section—

(1) The accelerate-stop distance is no greater than the length of the runway plus the length of the stopway (if present); and

(2) The takeoff distance is no greater than the length of the runway plus the length of the clearway (if present); and

(3) The takeoff run is no greater than the length of the runway.d in the Airplane Flight Manual for the elevation of the airport and for the ambient temperature existing at the time of takeoff;

§ 121.189 Airplanes: Turbine engine powered: Takeoff limitations.

(1) The accelerate-stop distance must not exceed the length of the runway plus the length of any stopway.

(2) The takeoff distance must not exceed the length of the runway plus the length of any clearway except that the length of any clearway included must not be greater than one-half the length of the runway.

(3) The takeoff run must not be greater than the length of the runway.

§ 135.379 Large transport category airplanes: Turbine engine powered: Takeoff limitations.

(1) The accelerate-stop distance, as defined in §25.109 of this chapter, must not exceed the length of the runway plus the length of any stopway.

(2) The takeoff distance must not exceed the length of the runway plus the length of any clearway except that the length of any clearway included must not be greater than one-half the length of the runway.

(3) The takeoff run must not be greater than the length of the runway

However please show me where it says we MUST use the CLEARWAY? As you have mentioned TWA, please tell me how you accounted for CLEARWAYS in the DC9? The MD90 doesn't have CLEARWAYS in the AFM, nor does the MD11.

I would be on a fool's errand if I did not increase thrust on the remaining engine (s) rather than hope to clear that ridgeline 7 miles away by 35 feet. I think that you have to look at NET and GROSS gradients.

TWA also did not assess more than 300 feet each side of the takeoff flight path (beyond the airport boundary), which was another reason for advancing to takeoff power in the event of an engine failure. We analyze 900 meters either side!

Are you talking about a particular aircraft type?

Mutt

aterpster

26th May 2010, 22:49

Mutt:

I didn't account for anything. I just did what they told me to do. But, I was on the union safety commitee and we got thinking about takeoff performance when they decided to operate our underpowered 727-200s into Reno.

They had their own performance and engineering department, which supposedly was "one of the best." We had no special OEI procedures anywhere. "Just climb straight ahead" was the party line. So, we put the union chairman's influence on the VP of operations, who agreed to give us the per mile performance data for the 727-200 (231 actually) for then Runway 25 at KLAS. We used runway-specific disposable takeoff charts, which each station stocked. Runway 25 was stated as being brake energy limited.

We selected a day where the temperature would just support MGTOW of 172,000 pounds. With an engine failure at V1 +1 knot it took 31 miles to reach 1,500 feet, afe. The airplane crashed into the first low ridge of mountains west of Runway 25.

Because of that, at Reno they changed the plan to use the slightly more robust 727-100 (131) and depart straight south on Runway 16 in the event of OEI. They did clear the ridge into the Washoe Valley and then planned a climb-in-hold at then WASHOE fix. Trouble is, they were 1,800 below the MRA for the crossing radial that formed the fix. They had failed to account for that.

So, I became a bit jaded about performance and engineering.

Many a day I made 727-231 takeoffs on Runway 8 at KABQ. In the days when we suppose to climb out straight-ahead in the event of OEI most of us were smart enough to know we had to turn right (some would have turn left because that is were the radar vectors went). I doubt we would have made it whether we turned right or left. In other words, circumstances seemed to indicate that they cooked the books, so to speak.

I realize today there is a nice advisory circular (120-91) but it is just that, advisory. And, as a TERPs sort of guy, my view is that it is a whole lot better than the monkey business TWA did, but it is stuck in the pre-RNAV/RNP closing years of the last century.

As to clearways and that stuff, I was never as worried about not stopping as I was about not making it past those mountains at places like ABQ, TUS, LAS, etc.

As to the equipment I flew it varied from awesome performance to inbetween that and poor:

707-100 and 300.
DC-9-10
727-100 and low-powered -200.
767-200
L-1011 and L-1011-100.

john_tullamarine

26th May 2010, 23:06

When I used to be a real pilot (TWA) required us to increase power on the remaining engine (s) in the event of an engine failure after achieving V2 speed.

No problem there - the option to increase thrust to the rated limit (but not above) remains available. In your case the operator had so mandated - fine. However, that is a discretionary option adopted by the operator. There is NO regulatory or design standard mandatory requirement to do so. In the view of most of us, the potential hazards associated with pushing up the throttles in a high workload situation greatly outweigh the potential hazards of leaving them right where they are - given that the RTOW sums were based on that latter option.

They also taught at the school house that payload was predicated on reduced thrust with all engines operating and with takeoff power in the event of an engine failure.

I'm afraid that is just so much engineering nonsense on the part of your instructors -

(a) if you start the takeoff reduced thrust then there is no procedure available to base an RTOW on the pilot's manually increasing the throttle setting. Indeed, the design standards specifically preclude such action in terms of required pilot procedure.

(b) following on from (a) your instructors' statement would imply never going with reduced thrust

(c) the option to increase thrust is there - mainly, I suggest, as a comfort factor to the operating crews back in the early days of reduced thrust takeoffs - certainly, I recall Wal Stack was very empathetic to such concerns in the 60s.

However, I leave it to you to produce a rational engineering argument to rebut my heretical position ?

I would be on a fool's errand if I did not increase thrust on the remaining engine (s) rather than hope to clear that ridgeline 7 miles away by 35 feet.

Common misconception. As mutt observes, you are looking at the calculated critical net surface case which has little to do with the pilot's world. The aircraft in the real world will do substantially better approximating or exceeding the gross surface case (unless you are having a REALLY bad hair day in which case you might eat a tad into the gross to net margin. You should expect to be a LONG way above that seven mile ridgeline as you cross over even if the net calculation were based on a minimal clearance back in the office.

I recall, in AN, John Walsh and Roger G quoting something like 1:250,000 probability of a critical OEI failure case's getting down to the net path. While I suspect that that figure might have involved some poetic pilot training licence, it sort of gives you an idea of the relative values of gross and net surfaces so far as the pilot might be interested.

TWA also did not assess more than 300 feet each side of the takeoff flight path (beyond the airport boundary), which was another reason for advancing to takeoff power in the event of an engine failure.

I can only hope that that statement is an aberrant misconception. The takeoff flightpath obstacle trapezoid is considerably larger - perhaps you can cite the operating standard to which the operator matched its ops engineering calculations ? All jokes aside, though, the trapezoids are NOT overly generous and the pilot needs to apply extremely strict attention to flight path tracking in any obstacle critical escape. Indeed, there has been sufficient simulator studies over the years to show, quite clearly, that mistracking IS a very real concern in the event of an unbriefed takeoff failure.

Really .. if you only had escape protection to 100 yards, your buddies would have had severe near misses in the real world failure case with close in obstacles ... I suspect that the tale is in the league of OWT perpetuated in the classroom ? However, please do provide authoritative support and we will recant our heresy.

we should not advance any thrust levers until we go to MCT if using fixed derates

That raises a point in philosophical difference. Indeed the takeoff thrust can be less than the continued climb thrust. While this might be fine from an engineering standards point of view, I prefer Wal's approach with his QF buddies. He related a tale about a crew's complaining that the F/E had pushed up the throttles to achieve METO/MCP - after a few seconds' thought, he concurred and, thereafter, the minimum flex level was climb thrust.

Are you sure your full thrust Vmca is below your fully derated V2?

The mutts, OSs, and JTs of the world like to keep the Vmca bogeyman in the thought processes just so that the newchums end up with a rational respect for those low speed lines in the sand. However, the line pilot should adopt a pragmatic approach - Vmca, generally, is way below your V2 and not a major concern unless one mishandles the failure grossly.

including V2 which can vary by as much as 40kts

While I can't comment on the 40kts as that would be specific to your particular bird, there is no problem with V2 varying - perfectly normal. However, you don't bring V2 below V2min for the day.

deck angle would be limiting, thus we accepted a speed well over V2

Unless such is mandated in the AFM takeoff performance section, it will be an operator discretion matter.

However, for the takeoff failure case, the problem is not so much well after the liftoff (which is where you might have limited the rotation angle) but during the takeoff flare rotation (ie a V1 or VR failure point). Having done a reasonable amount of work on this point in sim exercises, the case of min weight, aft CG takeoff (with a half realistic sim dynamic model) is the stuff of horror for the pilot until he/she has had several goes to get on top of the gyrations.

The main problem is that most pilots NEVER get to see the sort of aircraft response in this scenario as it is not routinely looked at in endorsement and recurrency training. Certainly opened the eyes for a few of my sim folk in years gone by.

common sense said to accept a speed greater than V2

In the extreme case that might be embarrassing in the case of a late first/early second segment critical obstacle ?

please tell me how you accounted for CLEARWAYS in the DC9?

(if I might fill in the background reason for the question) .. being that the DC9 AFM only provided BFL takeoff data so clearway was irrelevant to the matter.

"Just climb straight ahead" was the party line

No problem with that philosophy. However, commercially, it doesn't make sense as there will be runway cases for which it is commercial stupidity when, say, a turning escape might provide a LOT more weight.

With an engine failure at V1 +1 knot it took 31 miles to reach 1,500 feet, afe.

Now, that's pretty good. For the DC9 a critical takeoff might be closer to 50 miles for similar conditions .... [Caveat - as before, we are talking net so the real world pilot observation is considerably better than that pessimistic scenario].

The airplane crashed into the first low ridge of mountains west of Runway 25.

We would probably need some more details to comment. However, if the circumstances were an engineering mistake, then one should identify it, fix it, and make sure it doesn't happen again ...

They had failed to account for that.

Again, we would need more details to comment specifically but our discussion should be predicated on a presumption of competent ops engineering folks doing the work ...

So, I became a bit jaded about performance and engineering

and, by the sound of things, perhaps with good reason. Now, if we can interest Centaurus in this discussion, he has some real terror anecdotes on the subject in his archives ...

circumstances seemed to indicate that they cooked the books

can't speak to your circumstances but some of Centaurus' anecdotes relate to precisely that problem ...

.. and, should you perceive that mutt and I are giving you a hard time, we aren't. However, the youngsters need to be exposed to the good and the bad - there is still far too much in the way of OWT on this subject in the Industry.

Well done on a, no doubt, successful flying career - now to fishing, drinking and other fine activities more appropriate to the senior group.

Big Pistons Forever

26th May 2010, 23:50

I think it should follow that if airlines can run engines on condition untill they show wear, rather then TBO...GA aircraft should be able to do it as well..

And while we are at it, in our corporate operations, just like the airlines, we hire our own mechanic to determine engine condition...

Something tells me though...with the boss in the back, being sold on the idea of never having to pay for engine overhauls, might rethink this is I pull up right at the fence(because I calculated balanced field into the overrun)..

(Sorry just saw 'Flying Cheap' on Frontline)

A bit off topic but I feel I had to jump in. Under no circumstances should reduced power takeoffs be performed in light aircraft, partularly those with turbocharged engines. The extra fuel flow schedualled at the full power throttle position is vital for engine cooling and in any case every light aircraft POH I have seen has specified "full power" for takeoff.

Air Tourer

27th May 2010, 03:17

Just a minute. "under no circumstances" is a bit much.
For starters, the PW 985 (450hp) kept blowing heads of at red line MP.
The cure was never over 35", and 30" at lift off.

In a IO 520 Cont. (300hp) any low weight TO I did was climb power only.
I had CHTemp and E.gas temp fitted. All my engines went well over usual overhaul times by legal extensions. The real temp/fuel flow problems were low/hot/and heavy, and then we upped the fuel flow a couple of GP hour. Yeah, we used our common sense, not some homily thought up in an office. :rolleyes:

galaxy flyer

27th May 2010, 03:18

J_T

I do believe that 300 feet lateral clearance was the FAR 121 standard for the OEI case at one time, cannot say for now or post AC 120-91.

GF

john_tullamarine

27th May 2010, 04:27

I do believe that 300 feet lateral clearance was the FAR 121 standard for the OEI case at one time,

ah, my knowledge base increases in the usual exponential fashion .. as you are aware my background is not in 121. Thanks for the heads up.

From an engineering and operations viewpoint, I take the position that 300ft lateral is somewhere between unachievable and incomprehensible without LLZ-accuracy electronic track guidance ....

mutt

27th May 2010, 06:22

aterpster, your list of aircraft are all old generation aircraft,

707-100 and 300.
DC-9-10
727-100 and low-powered -200.
767-200
L-1011 and L-1011-100.

So whilst they had limited performance capabilities, they also had limited computerized takeoff performance from the manufacturers, we operated the 707,727,L1011 and MD90...... our ability to calculate exactly what the aircraft was capable of doing was extremely limited and time consuming.

With new generation aircraft we also got new generation software, including electronic airplane flight manuals. The situations that you have detailed for LAS and RENO, need not exist today.

When we had those fleet aircraft in service, we didnt have FIXED DERATES, they only operated with ASSUMED TEMP/FLEX, this meant that the VMCG speeds were based on the thrust at actual temperature and you could advance the throttle if so desired. However today, we are operating aircraft at 55% of their available takeoff power with a VMCG associated with that THRUST RATING, so any attempt to advance the throttle at lower speeds, could result in an undesired situation.

Another question, if you aircraft was capable of achieving 231 feet/nm and you wished to climb to 1500 feet, why did it take 31 nms? Why not use extended second segment and climb to 1500 feet before accelerating? YOu would make less noise that way :):) (i.e not hit the mountain.)

Mutt

john_tullamarine

27th May 2010, 06:49

mutt,

Surely you bored yourself to tears, on occasion, running regressions or lookup tables to computerise the paper AFM sheets ? With those we could run off pretty accurate RTOW tables in a few minutes ...

Likewise we used the 50nm bogey for the DC9 to get the message across that OEI net climb was not startling ...

Denti

27th May 2010, 07:17

we should not advance any thrust levers until we go to MCT if using fixed derates

That raises a point in philosophical difference. Indeed the takeoff thrust can be less than the continued climb thrust. While this might be fine from an engineering standards point of view, I prefer Wal's approach with his QF buddies. He related a tale about a crew's complaining that the F/E had pushed up the throttles to achieve METO/MCP - after a few seconds' thought, he concurred and, thereafter, the minimum flex level was climb thrust.

Many of my colleagues would love that restriction as it is allways somewhat funny to see an increase in thrust on climb-thrust reduction. The 737 offers two fixed reduced climb thrust settings based on max rated thrust. So using derate take-off thrust combined with assumed temperatures can lead to quite substantially less thrust than the lowest (climb 2) climb thrust setting.

Are you sure your full thrust Vmca is below your fully derated V2?
The mutts, OSs, and JTs of the world like to keep the Vmca bogeyman in the thought processes just so that the newchums end up with a rational respect for those low speed lines in the sand. However, the line pilot should adopt a pragmatic approach - Vmca, generally, is way below your V2 and not a major concern unless one mishandles the failure grossly.

Sadly we do not even get any tables concerning Vmcg/a anymore, they were all removed because "the software only provides safe combinations, you don't need to worry", but on the other hand we get told "do not ever advance thrust levers if using a fixed derate".

including V2 which can vary by as much as 40kts

While I can't comment on the 40kts as that would be specific to your particular bird, there is no problem with V2 varying - perfectly normal. However, you don't bring V2 below V2min for the day.

Exactly what i was trying to say, thanks for clarifying it. It seems V2 was rather fixed for aterpster when in reality it is a very flexible thing within its limitations.

By the way, with V2s as low as 1 to 2 kts higher than Vr it will be an interesting example in precision flying to keep that speed during rotation and beyond with the kinda lowish rotation speed required for stretched bodylength-aircraft (738/9).

rudderrudderrat

27th May 2010, 07:53

Hi Mutt,

Why not use extended second segment and climb to 1500 feet before accelerating? We started flying some old 707s on short haul charter routes in the 70s. The previous operator of these aged aircraft had "trained" our new trainers to use 1,000 ft agl Acceleration Altitude everywhere. When our performance people looked at the available weights out of certain airfields with terrain problems, they produced performance tables with raised AAs so we could increase our payloads.

The previous operator had never considered raising the AA.

aterpster

27th May 2010, 10:01

John Tullamarine:
Well done on a, no doubt, successful flying career - now to fishing, drinking and other fine activities more appropriate to the senior group.
Thus far I have mixed some of those retirement activities with a continuing involvement as a consultant in TERPs as it evolves into performance based navigation (PNB), the most advanced iteration of which is RNP AR. I work with an associate who is also heavily involved in takeoff performance issues. There is a crossover, though, when I see how far behind OEI takeoff flight path navigation is from the other work we are doing.

As to my flying carrer, I was very happy the day I no longer had to fly those TWA 727s out of places like ABQ. After many years of flying that airplane into that station, it was a real pleasure to make my first departure on Runway 8 in a 767. It brought back fond memories of the early days of departing Runway 8 as a F/O on the 707-100B (fan engines, as opposed to those awful "water wagons.")

And, as to net vs. gross, I have understood that for years. My hunch was that TWA's 727-200s with the smallest engine Boeing optioned, would have been more in the arena of net than gross.

aterpster

27th May 2010, 10:05

galaxy flyer:
I do believe that 300 feet lateral clearance was the FAR 121 standard for the OEI case at one time, cannot say for now or post AC 120-91.

It still is. 200 feet within the airport boundary, 300 beyond.

Advisory Circular 120-91 is a big improvement, but it is nonetheless not mandatory. And, the navigation concepts are way behind the times.

Centaurus

27th May 2010, 11:03

However on B737s, emergency turns at V2 banking into the failed engine may be fatal if unaware of spoiler turn assist problems.
Not banking into the good engine may drastically reduce the Vmca on which V2 minimum is calculated from.
So if you have the choice,turn into the good engine as it is how Vmca was calculated in the first place.(3-5 degrees).

I wonder if Boeing flight department are aware of these dangers? if so, why is there no mention of this advice in the B737 flight crew training manual? Maybe because Boeing believe the alleged "dangers" are statistically insignificant?

de facto

27th May 2010, 12:05

Centaurus,

Boeing knows.
I am pretty sure that V2 min is based on VMCAx1.1 and Vr is based on 5% less than Vmca.
Of course VMCA was demonstrated/calculated by using full rate thrust,empty aircraft and most aft CG.,and BANK into good engine..so on line you normally get more margin as you normally use derate,have a rather centered CG and heavier.

Denti

27th May 2010, 12:16

Derate has different VMCg/a values. So using a derate won't increase your margin. Assumed temperature on the other hand does ans the VMC values are based on full rated thrust for the selected thrust rating.

de facto

27th May 2010, 13:26

Denti,

I agree with the requirement NOT to increase thrust to the full rate thrust following an engine failure during/after a derate T/0.
If you fly at full rated thrust,aft CG,light weight,and you DONT bank into the good engine,your actual Vmca will increase,with the possibility of your actual speed being below the set VMCA for your engine thrust setting.(derate or not).Derate gives a lower VMCA.
The problem comes when engine failure turn require to bank 15 at V2 due to obstacles (worse scenario left turn with a left engine failure).Problem being increased by the spoiler assist design during turns.

When flying at VMCA(aircraft cant maintain the heading), Reducing the thrust on the good engine, isnt a way to recover the aircraft control by reducing the assymetrical force?(if rudder and ailerons are not effective
enough during take off?).
From Avioconsult:
'The actual VMCA can also be lower – safer – than the AFM published VMCA though, for instance when the asymmetrical thrust is not as high as used during VMCA testing or the cg is forward. VMCA can also be lower than stall speed VS in which case the airplane is said to be controllable down to the stall, which however does not apply for all bank angles.'

galaxy flyer

27th May 2010, 14:16

J_T and Mutt

Here is the relavant passage in FAR 121.189 relating to take-off path:

2) In the case of an airplane certificated after September 30, 1958 (SR 422A, 422B), that allows a net takeoff flight path that clears all obstacles either by a height of at least 35 feet vertically, or by at least 200 feet horizontally within the airport boundaries and by at least 300 feet horizontally after passing the boundaries.
(e) In determining maximum weights, minimum distances, and flight paths under paragraphs (a) through (d) of this section, correction must be made for the runway to be used, the elevation of the airport, the effective runway gradient, the ambient temperature and wind component at the time of takeoff, and, if operating limitations exist for the minimum distances required for takeoff from wet runways, the runway surface condition (dry or wet).

Which what aterpster is referring to. Yes, a ridiculous standard of performance, especially with regards to using 400 feet AFL as a standard acceleration height. BTW, I happen to know him by reputation and reading and, at least, one very good bit of advice via email on MVAs :ok:

GF

Firmly resisting any excursions in Vmcg discussions!

aterpster

27th May 2010, 15:16

mutt:
aterpster, your list of aircraft are all old generation aircraft

Well...the 767 is still rolling off the Boeing assembly lines, albeit with a lot better FMS. But, many airlines operate exactly the same version of the 767 I flew and with their fleet mixed with the Pegasus 767.

With new generation aircraft we also got new generation software, including electronic airplane flight manuals. The situations that you have detailed for LAS and RENO, need not exist today.

I don't see where today's "gee wiz" stuff has improved the OEI case all that much. The big improvements are better autopilots (but not that much better than the 767 I flew) RNP AR, LPV, RVSM, EGPWS, and TCAS. Auto checklists are great, too. Electronic charts are just a vector graphics presentation of a 1950s chart. Until database charts arrive, there is not much improvement there, other than pilots not misplacing paper charts.

Another question, if you aircraft was capable of achieving 231 feet/nm and you wished to climb to 1500 feet, why did it take 31 nms? Why not use extended second segment and climb to 1500 feet before accelerating? YOu would make less noise that way (i.e not hit the mountain.)

The last thing I would do is improvise the takeoff flight path profile in the event of OEI. TWA mandated clean-up at 1,000 feet, and that is what we did. (They used 800 feet in the earlier days). So, the 31 mile performance data they provided to our safety committee was based on clean up at 1,000. In any case, there is no way, no matter what you did, that 727 would have cleared the second range of mountains west of KLAS.

Next, a friendly poke at you engineers: in mountainous terrain their are more holes than in Swizz cheese in the calculation/guidance in the en route climb requirements from completion of the end of the takeoff flight path until reaching the effective minimum safe instrument altitude. And, Part 121 is ancient in still requiring 5 miles each side of centerline for OEI en route. On the one hand that regulation mandates only 300 feet each side centerline for the takeoff flight path, but it requires an absurdly wide 5 miles after the takeoff flight path. I don't see anyone doing an adequate job on the en route climb phase.

Finally, since I work with RNAV issues in my present life, we (industry and FAA) are constantly finding inconsistencies in FMS implementation issues across the larger fleet. And, in spite of what you imply, much of today's U.S. air carrier fleet consists of aircraft no more capable than the old-generation 767 I flew. In fact, one of the very big airlines cannot fly LNAV/VNAV IAPs because they don't train their crews because of these mixed fleet issues (i.e., a whole lot of the older segment of their fleet does not have GPS sensing, rather they have DME/DME updating which I used in 1984.) (The OEMs charge a fortune to update FMSes.)

mutt

27th May 2010, 16:57

300 feet horizontally after passing the boundaries. Thats the FAA cone, the ICAO cone is wider, we decided to use the wider cone as its more practical. We had technical advice from TWA for many many years, so I guess that the 800 feet MFRH which we presently use came from them, although that is increased if limited by obstacles.

The 767 came with Mark7 performance software which is extremely limited in its capabilities, hence the reason i consider it an old generation aircraft.

The "gee whiz" that came with newer aircraft is our ability to calculate takeoff flight paths with greater accuracy, we can also account for wind from various quadrants. We end up suffering from greater payload reductions than required by regulation, but we are satisfied that OEI procedures can be flown under all circumstances.

As for the mountainous terrain, whats wrong with turning the aircraft around and returning it to the airport? We have a habit of ending OEI procedures over a defined point in order to ensure that all obstacles are accounted for, rather than jump into a 5 mile cone without accurate information.

I don't see anyone doing an adequate job on the en route climb phase. Very true......but with the introduction of BCOPS and PEP that might change.

Mutt

Pugilistic Animus

27th May 2010, 17:20

Very true......but with the introduction of BCOPS and PEP that might change.

What's that ?:)

aterpster

27th May 2010, 17:36

mutt:
As for the mountainous terrain, whats wrong with turning the aircraft around and returning it to the airport? We have a habit of ending OEI procedures over a defined point in order to ensure that all obstacles are accounted for, rather than jump into a 5 mile cone without accurate information.

As to accurate information, 1:24,000 topo quads are available for the entire U.S., except Alaska which is (I believe) still pretty good with 15 minute quads. In other parts of the world the data are limited to a varying degree, in spite of the U.S. taxpayers having spent a bundle on the Shuttle mission that obtain good topo data.

As to turning around and landing, that often is not a very good idea. Even when it's day VFR some mountain airports have a severe balked landing obstacle environment. So, the crew may want to proceed, for example, to Montrose or Grand Junction rather than returning to Aspen, Eagle, Hayden, Gunnison or Rifle.

If the weather is IMC the departure may have been made at standard takeoff minimums, which are usually well below landing minimums in the mountains. And, that often holds true even at many flat-land airports, thus the requirement for two-engine bird to have a takeoff alternate in such circumstances.

Further, in the mountains, the end of the takeoff flight path may be too low to turn around in either VMC or especially in IMC to get to the appropriate instrument approach procedure IAF.

Very true......but with the introduction of BCOPS and PEP that might change.

Don't know those acronyms. :)

aterpster

27th May 2010, 18:19

J_T and Mutt:

War-story department: One of my pals was flying a flight out of KABQ on a hot summer day (wx CAVU). It was a 727-100 (20,000 pounds less max structural weight than the -200, but with the same engines). As I recall they were at MGTOW of 152,000. Fortunately, they were taking off on Runway 26 (which descends to the Rio Grande River west of the field). On rotation they shedded a tire into one of the outboard engines, which of course failed in a nasty manner. Being sharp guys, they briefed the OEI profile again and found that the airplane just hung at zero climb rate at V2, then the speed started to slowly decay. So, the PF dropped the nose to regain speed (that would have been a hull loss on Runway 8) and then gently banked left to turn south along the river. The airplane then managed to stay level at somewhat over V2 then after a few miles very slowly began to climb. They went south about 20 miles before they could clean up, at which time performance picked up and they were able to climb sufficiently to turn around and return to the field.

That one was kept real quiet.

I believe it was the awesome reliability of jet engines that kept us from disaster over the years. I had three engine failures (or mandatory shut-downs) over 27 years, and only one was on takeoff (L1011 center engine failed at 2,900 agl after clean up to 250 knots.)

john_tullamarine

27th May 2010, 23:22

This thread is cranking up to be quite interesting ...

can lead to quite substantially less thrust than the lowest (climb 2) climb thrust setting

It would be more logical to me, if you wish to use max derate/flex, to continue at that setting until it becomes limiting with respect to climb thrust.

Sadly we do not even get any tables concerning Vmcg/a anymore

You really don't need them per se .. look to the speed schedule tables at minimum weight. Where the speed no longer varies with weight (Vs limiting) you are either Vmca or Vmcg limiting.

when in reality it is a very flexible thing within its limitations.

Basically fixed at very low weights to Vmca limitations, then increases with Vs against weight with the proviso that a modest increase (per overspeed -Boeing, improved performance - AB) for better climb performance usually is available

to keep that speed during rotation and beyond with the kinda lowish rotation speed required for stretched bodylength-aircraft (738/9).

Keeping in mind that V2 is OEI driven.

For the normal AEO takeoff, one isn't looking to peg V2, rather something modestly in excess - typically +15-25 according to AFM recommended practice for twins. Especially for the sports car twins, AEO V2 climb has its own potential for hazard and frightens the daylights out of the new passengers ..

"trained" our new trainers to use 1,000 ft agl Acceleration Altitude everywhere

Common practice to use a standard third segment height for crew familiarity (other than for the nastier places which require specific special escape procedures). Generally, the standard height will be based on the highest runway requirement outside the set of special procedures. eg, in Australia we used (and probably still do) 800ft which was based on Canberra obstacles.

when I see how far behind OEI takeoff flight path navigation

I don't have any problems with cutting down the trapezoid a bit .. with two caveats -

(a) how do we ensure the higher manipulative standard to ensure accurate tracking in the initial OEI phase ?

Plenty of sim studies to show that the reality doesn't match the desire, even with generally high standard of manipulation crews.

It certainly CAN be trained in but that takes time and money. In my experience, one needs a directed sim session's worth of time to achieve a standard where the pilot can reliably back track the opposite localiser from a min weight Vmcg/Vmca limiting takeoff (aft CG .. the full bit) .. but it's wonderful to see the confidence boost once the guy/gal up front gets to that standard. Conversely, most who haven't been exposed to those extremes tend to roll over and go in upside down on the first couple of attempts ...

(b) the aircraft has to have a nav system of sufficent statistical accuracy and reliability to warrant permitting stooging down near and around obstacles

.. with both satisfied all is OK.

I recall my own Damascus .. coming to airline flying as an ops engineer, I had great faith in the engineer's ability to generate wonderful and interesting takeoff and escape data ... the first max weight takeoff in the F27 from a critical length runway ... as I watched (with ever widening eyes) the runway head slide under the radome .. and we were still on the ground .... caused me to adopt a far more conservative approach.

Now that another colleague on this forum is flying rather than computing, I suspect that his views progressively will echo my own ....

My hunch was that TWA's 727-200s with the smallest engine Boeing optioned, would have been more in the arena of net than gross.

That does suggest a bit of over optimistic ops engineering .. the engine Mk should only dictate the numbers for the standardised conditions ...

It still is. 200 feet within the airport boundary, 300 beyond

Then I am glad that I have never worked to 121.

As to accurate information, 1:24,000 topo quads are available for the entire U.S

Having spent much time poring over topos of many and varied scales, and following up with the theodolite slung over the shoulder on numerous occasions .. I don't view anything much worse than 1:5000 - 1:10000 as being other than indicative

So, the crew may want to proceed, for example, to Montrose or Grand Junction rather than returning to Aspen, Eagle, Hayden, Gunnison or Rifle.

Concur .. but mutt's point is that, first, one needs to get high enough to do so. That's where the option of limiting the radius of action (often) provides an advantage.

the end of the takeoff flight path may be too low to turn around

Many of us adopt the practice of running the takeoff calcs up to enroute - certainly OS and I do in the present group. To do otherwise in other than terrain benign environments would be hard to argue successfully in court.

War-story department:

I look forward to an ale or 10 over which the group can exchange a set of similar horror stories.

We just have to accept that the certification data is idealised with few sops to the conscience of reality. On bad hair days, stuff happens to conspire against the crews ... as you observe, systems reliability is a saving grace.

Mad (Flt) Scientist

28th May 2010, 00:35

I am pretty sure that V2 min is based on VMCAx1.1 and Vr is based on 5% less than Vmca.

Only for specific cases where VMCA is the determining factor for V2min. It can just as easily be based on stall speed ratios, or any of several other factors.

That's why the perf engineers get paid to do what they do, and why they discuss the niceities of it so often - it's not simply deterministic, and can be quite a convoluted story in reality.

john_tullamarine

28th May 2010, 00:54

it's not simply deterministic, and can be quite a convoluted story in reality.

.. especially if one doesn't have a nice OEM package and has to work out what the AFM really is trying to do .. all the while keeping an eye to the frozen design standards relevant to the Type ... it does have its moments.

aterpster

28th May 2010, 01:59

j t:

I don't have any problems with cutting down the trapezoid a bit .. with two caveats -

(a) how do we ensure the higher manipulative standard to ensure accurate tracking in the initial OEI phase ?

Plenty of sim studies to show that the reality doesn't match the desire, even with generally high standard of manipulation crews.

Well, with the modern birds that you see populating the fleet, there are a fair number with triple IRUs, dual GPS sensors, dual (or triple) FMSes, and dual auto-flight. These are the type of aircraft than can (and are often certified for RNP AR values of 0.11 if not 0.10.).

RNP AR requires 2 X the RNP value, but for OEI purposes it could be 1 X RNP. The trapezoid would splay from the DER to the 1 X RNP value. The OEI flight path would be database driven and would have RF legs (limited to 15 degrees of bank, or less) for any track changes.

That would be the real magic from today's high-end technology.

john_tullamarine

28th May 2010, 02:16

there are a fair number with triple IRUs, dual GPS sensors, dual (or triple) FMSes, and dual auto-flight

No problem with any of that for the latter stages of takeoff, enroute and landing .... JBs have always impressed the daylights out of us all and I'm not immune to gee whiz stuff any more than the next fellow.

However, how do we effect the transition from manual flight to autoflight during the early takeoff stage in a manner which doesn't see the manual bit go outside whatever shape/dimension the trapezoid may be in a critical case with, shall we say, average pilots rather than those who might qualify for "Ace of the Base" brevets ?

de facto

28th May 2010, 03:52

Scientist,JT

V2 min is based on 1.1VMCA or 1.23 VS whichever is higher right?

JT when you mentioned that one could find out whether VMCA/G limited by checking the 'the speed no longer varies with weight (Vs limiting)'.
Are you talking about the Perf tables where you get the ASSUM temp?or the tables in the FCOM where you get the speeds for the actual weight(balanced field)?

Quote:'That's why the perf engineers get paid to do what they do, and why they discuss the niceities of it so often - it's not simply deterministic, and can be quite a convoluted story in reality.'Unquote

I am getting lost, could you please use a more basic english?and I would love to be able and follow this very interesting debate with my ICAO 5.8:E

Thanks!

john_tullamarine

28th May 2010, 05:19

V2 min is based on 1.1VMCA or 1.23 VS whichever is higher right?

Variation exists depending on the particular Standard but the general rule applies that the minimum takeoff speed (either V2 or VTOSS) is the greater of a Vmca and Vs factor.

JT when you mentioned that one could find out whether VMCA/G limited by checking the 'the speed no longer varies with weight (Vs limiting)'.
Are you talking about the Perf tables where you get the ASSUM temp?or the tables in the FCOM where you get the speeds for the actual weight(balanced field)?

You're looking for a table which gives V1/VR/V2 against RTOW. At the lower weights, for most aircraft, Vmca or Vmcg will become limiting rather than Vs. You see this change when the speed no longer gets lower with reducing weight.

I am getting lost, could you please use a more basic english?

Any time we talk too much jargon and you don't understand, the fault is with us, not you. Just ask and we will try again and rephrase the discussion.

it's not simply deterministic, and can be quite a convoluted story in reality

MFS' meaning here is that it is not just a matter of looking up a table to get the answer. For the RTOW calculation one has to run a series of calculations to check a range of limitations with the most limiting (ie lowest RTOW answer) becoming the final RTOW for the conditions. That process, depending on the aircraft, the runway, and how much effort one wants to put into optimising the result (getting the highest RTOW) can get quite involved and complicated (convoluted)

de facto

28th May 2010, 06:51

Thank you:ok:

arba

28th May 2010, 07:51

FCTM 737 :

- Limit bank angle to 15deg. when speed less than V2+15 kts.

Denti

28th May 2010, 07:57

can lead to quite substantially less thrust than the lowest (climb 2) climb thrust setting

It would be more logical to me, if you wish to use max derate/flex, to continue at that setting until it becomes limiting with respect to climb thrust.

Dunno if that is even possible. The FMC "reduces" thrust to climb thrust setting at a predetermined height above aerodrome. You can change the setting at which height that is for all engines or one engine out, but you cannot put any other limit based on thrust in there.

Sadly we do not even get any tables concerning Vmcg/a anymore
You really don't need them per se .. look to the speed schedule tables at minimum weight. Where the speed no longer varies with weight (Vs limiting) you are either Vmca or Vmcg limiting.

Well, no speed schedule tables either. Its all in the software for take off performance calculation. Only inflight and landing tables are available for non-normal consideration. And once you get dual figure V1s on a 50t+ aircraft you begin to wonder...

when in reality it is a very flexible thing within its limitations.

Basically fixed at very low weights to Vmca limitations, then increases with Vs against weight with the proviso that a modest increase (per overspeed -Boeing, improved performance - AB) for better climb performance usually is available

Especially during low weights you have the biggest differences. For example on a lightweight -700 and a 4000m runway you can have V values in the lower 120s, but if you add assumed temperature and improved climb consideration into the mix you can end up using all of that runway with V1/Vr in the 160s and V2 in the 170s. Not really fun to fly the latter thing as you use around a minute of take off run and all of that available runway, not to mention you cannot pitch up more than 7 to 8° after liftoff because you run out of airspeed if you do.

Keeping in mind that V2 is OEI driven.

For the normal AEO takeoff, one isn't looking to peg V2, rather something modestly in excess - typically +15-25 according to AFM recommended practice for twins. Especially for the sports car twins, AEO V2 climb has its own potential for hazard and frightens the daylights out of the new passengers ..

Of course it is OEI driven. But even in the simulator during OEI practice i would be interested to see someone peg a V2 that is only 2 kts higher than Vr. Especially when the advise in the FCM is to rotate around 1/2° per second slower than during AEO take offs resulting in rotation rates around 1 to 1,5° per second. Just checked though and any speed after rotation between V2 and V2+20 is ok, so that seems to cover it.

de facto

28th May 2010, 08:17

Arba,

please reread my post#60.

ETP designed to be flown at not more than V2 due to obstacles/noise when being in a light,aft CG aircraft and having to turn on the side of the failed engine and not banking 3-5 degrees away from the bad engine,with also spoiler turn assist on 737s can lead your aircraft to become uncontrollable and leading to a disaster.

VMCA was determined using bank into the good engine,using the boeing technique of using rudder to get the control column in the neutral position(bank) does not satisfy the requirement of maintaining a demonstrated VMCA in case of a minimum V2 take off.
Therefore the possibility of losing control.

john_tullamarine

28th May 2010, 11:01

Well, no speed schedule tables either

If your software permits playing a bit, try running a series of calculations for reducing weights down to the APS typical weight. You will probably see the effect towards the lower weight end in the output.

you can end up using all of that runway

While some operators do this .. you can also limit the optimisation to give you a pad. For instance, you could use data for an intersection but actually takeoff from an earlier entry point or limit the flex temperature. If you have more user flexibility in a particular program, you probably can limit arbitrarily the runway lengths to provide whatever pad you choose. Talking what ifs here, of course .. operator SOP probably limits your real world flexibility.

i would be interested to see someone peg a V2 that is only 2 kts higher than Vr

Using the OEM AFM techniques, you should be able to peg the AFM recommended V2 OEI without too much difficulty. The VR/V2 relationship includes consideration of the speed increase OEI. If you have a failure prior to VR you should expect to end up someone near V2 towards the end of the rotation sequence. If the rotation is AEO and then you have a failure in the initial climb, you would normally expect to see an AEO speed overshoot (+20-25 being typical). You would then prefer to hold the overspeed to take advantage of the improved climb ... the AEO bit will have put you above the OEI profile so all should be well. My comments may not apply to specific aircraft but will be fairly general in application.

does not satisfy the requirement of maintaining a demonstrated VMCA in case of a minimum V2 take off.

Given that you won't know the precise details of what the certification flight test folks did, you can only work on the basis of what's in the AFM guidance material. If you comply with that guidance, you can presume that the OEM has considered all relevant matters including turns and Vmc effects.

aterpster

28th May 2010, 13:27

j_t:
However, how do we effect the transition from manual flight to autoflight during the early takeoff stage in a manner which doesn't see the manual bit go outside whatever shape/dimension the trapezoid may be in a critical case with, shall we say, average pilots rather than those who might qualify for "Ace of the Base" brevets ?

No doubt we have seen that to be such a serious problem in normal ops that, in some cases, RNAV SIDS have been cancelled by the FAA at some major air carrier airports because of the variance in LNAV capture capabilities and pilot fat thumbs.

But, with an RNP AR capable airplane the transition should be smooth and comparatively easy, with LNAV track already being computed by the FMS and ready for engagement either to the FD and/or autoflight. And, if the aircraft has auto-rudder it's no different than the early stages of any liftoff after completion of the takeoff roll.

OTOH, if the pilot has to input rudder manually, and cannot remain within the splay from the DER to the linear RNP containment area then we have some pilot skills that are unsatisfactory. :) I have that concern today about circumstances where pilots have to perform in "unusual" situations other than just OEI just after V1.

My premise is taking full advantage (touted earlier in this thread) of the state-of-the-art technology on more than a few airframes today. For example, with such technology an OEI containment route can be developed for Aspen Runway 33 that is devoid of rising terrain until almost to Glenwood Springs. (some 27 OEI flight-path miles.)

john_tullamarine

29th May 2010, 10:44

Then we concur in respect of the critical problem .. the initial bit.

My observations in the sim in a previous life suggest that there is a BIG need for a LOT of training work to be done before we put aircraft at risk in a reduced obstacle trapezoid scenario ? I have no doubt that just about any half competent pilot can be trained to have a high probability of containment in critical cases ... I just have a concern that the operators won't want to spend the money and effort in the absence of a lot more control by the Regulators.

aterpster

29th May 2010, 15:21

j_t:
Then we concur in respect of the critical problem .. the initial bit.

My observations in the sim in a previous life suggest that there is a BIG need for a LOT of training work to be done before we put aircraft at risk in a reduced obstacle trapezoid scenario ? I have no doubt that just about any half competent pilot can be trained to have a high probability of containment in critical cases ... I just have a concern that the operators won't want to spend the money and effort in the absence of a lot more control by the Regulators.

We concur except for the state-of-the-art birds that track LNAV while rolling and are ready to engage runway track on lift off and then have easily available the OEI procedure (which should be the same as the operator's normal all-engines-operating obstacle departure procedure at an airport like Aspen).

In any case, it is a bad airport, indeed, that has that type of close-in obstacle environment just beyond 300 feet each side of the DER. Even nasty Aspen has no threat until approximately 900 feet to the left of the extended runway centerline close-in.

john_tullamarine

30th May 2010, 10:51

state-of-the-art birds that track LNAV while rolling and are ready to engage runway track on lift off

Now do these use the autopilot to perform the takeoff or does Capt Pilot still do the initial bit ? If so, then we still have the problem of tracking integrity during a critical failure prior to autopilot engagement.

it is a bad airport, indeed, that has that type of close-in obstacle environment just beyond 300 feet each side of the DER.

.. and places where the runway points through a close in saddle or has an isolated close in hill feature with surrounding terrain necessitating an early turn either inside or around the hill ... not at all rare.

aterpster

30th May 2010, 14:36

j_t

Now do these use the autopilot to perform the takeoff or does Capt Pilot still do the initial bit ? If so, then we still have the problem of tracking integrity during a critical failure prior to autopilot engagement.

Training must have really gone down hill. We were required to keep it tracking on runway leading (and 767 runway track) especially during rotation and establishing V2 to V2 + 10. If not we remained for training.

WR: it is a bad airport, indeed, that has that type of close-in obstacle environment just beyond 300 feet each side of the DER.

.. and places where the runway points through a close in saddle or has an isolated close in hill feature with surrounding terrain necessitating an early turn either inside or around the hill ... not at all rare.

Some examples? Any in the U.S. Airports where 737 type aircraft operate?

rudderrudderrat

30th May 2010, 14:53

Hi aterpster,

I don't know about any US airports - but ACE - GCRR - Lanzarote in the Canary Islands has an engine out procedure from Rwy 03 that says something like "At 60 feet (I'll say that again sixty feet) - Right Turn 090 degs".
(Min height for turn = 1.5 * wing span)

I've taken L1011s & A320s in there.

bellcrank88

30th May 2010, 15:31

Slightly off topic, but could not find answers to these couple of questions?

QNH (Altimeter) tolerances for a RTOW calculation. If I am lined up to go and the altimeter setting drops 1 mb, am I covered? My company uses a 2 mb tolerance for reduced thrust TO, but is there a required tolerance for Max Thrust TO calcualtions?

Also I recall from Perf A that the headwind is factored by 50% and the tailwind by 150%. So what does this really mean. (ie what if I have 10 knots vs 0 knots?)

Mad (Flt) Scientist

30th May 2010, 17:39

Also I recall from Perf A that the headwind is factored by 50% and the tailwind by 150%. So what does this really mean. (ie what if I have 10 knots vs 0 knots?)

It means that the headwind credit used for the calculation is 50% of the (beneficial) effect and the tailwind effect used is 150% of the (detrimental) effect.

So a reported 10kt headwind is calculated as if the real headwind were 5kts, and a reported 10kt tailwind calculated as if the real tailwind were 15kts.

If the reported headwind is 10kts, and the real value drops below 5kts (such as to 0), your calculations lose all margin of conservatism wrt wind and you eat into "other" margins, if any.

Also, because the margin used for wind is proportional to the wind, with a high reported wind you have a fair margin. At near-calm conditions the margin is negligible (50% of 0 being 0)

john_tullamarine

30th May 2010, 22:43

Training must have really gone down hill. We were required to keep it tracking on runway leading (and 767 runway track) especially during rotation and establishing V2 to V2 + 10. If not we remained for training.

And, for routine failures (high gross weight, V1 .. the normal sort of sim thing) such is a walk in the park and just about any pilot can produce the required goods.

However,

(a) going back to some Australian DCA studies with a major domestic carrier many years ago in the sim ... for an unexpected failure, the reality was that a significant minority of pilots performed far worse with respect to tracking integrity than when they were primed for the failure .. and this for "easy" failure conditions

(b) some years ago I did a stint of contract work in the 732 sim for an operator which routinely flew (and trained for) high overspeed schedules. However, this operator also had at least one airport from which it routinely flew a short range positioning flight .. at min weight and min speed schedule .. but with no exposure in the sim.

I thought it might be interesting to see how folk fared with some increased difficulty (all in an appropriate, relaxed and friendly manner). The results I found very interesting. Even the more experienced checkies etc., had some difficulty until they'd had a couple of goes to get the gyrations under control.

As a note, this operator had modelled a large bird takeoff engine impact from the FDR and the sim responses appeared to be quite realistic to me .. sitting in the backseat, as I was, watching on ...

As we were doing a lot of initial command training (generally from 744 FO) I decided to spend some of the spare time in getting these guys and gals up to a higher than routine standard. In general, it took a very solid session (with absolute max use of freeze and reset) to move progressively back from the failure comfort zone and get to the stage where a min speed, min schedule, aft CG, worst failure (available on the box) situation (with the failure occuring during the early part of the rotation flare) could be handled with skill, dexterity and considerable aplomb .. including tracking out on the opposite end localiser .. indeed the folk could handle the situation without going to FSD during the failure .. which is pretty good in my view.

All good fun, lots of sweating in the front .. and the kids went home on a cloud of swelled head and confidence .. and slept that night like babies.

Might I be so impertinent as to suggest that you might ask to look at that sort of scenario in your next sim. Unless the sim setup is very benign in that corner of the envelope .. it is interesting.

Some examples? Any in the U.S. Airports where 737 type aircraft operate?

Can't speak to the US.

Several come to mind in Australia (CBR, HBA, for instance). Doesn't really matter .. just one is enough to defeat the philosophy you are espousing as a Standards consideration.

If I am lined up to go and the altimeter setting drops 1 mb, am I covered? My company uses a 2 mb tolerance for reduced thrust TO, but is there a required tolerance for Max Thrust TO calcualtions?

Generally we incorporate some calculation fat for pressure variations otherwise the Regulators might look at us over thick-rimmed school ma'am glasses during the audit ...

In practical terms, the effect for small Hp variations is pretty small. If you don't have any specific guidance then, presuming you do have some general chart information, say WAT limits, you can figure a notional reduce rate in terms of kg/100ft, say, and apply that for mum and the kids when looking up the RTOW data. The result will be pretty close to the sort of figure you might get by running the calculations with a minor difference in Hp input.

So a reported 10kt headwind is calculated as if the real headwind were 5kts, and a reported 10kt tailwind calculated as if the real tailwind were 15kts.

As a sideline note, if you have graphical data available, you can see this effect on the wind grid (if tabular, you might have to plot the graph yourself) in that the slope of the lines (as W/C varies) changes at zero wind .. the effect is small for light weights/distances but quite noticeable at the other end of the envelope.

bellcrank88

30th May 2010, 23:46

Mad Scientist,

I know what the formula numbers are, my question is - is there really no factor at all if you are using no wind? Yes the math says there isn't, but practically it doesn't really make sense that if you then have a 1 knot tailwind you are no longer covered.

I have never seen a heavy stop to check the TO data when the QNH drops 1 mb. Is there really no factor in a max RTOW?

john_tullamarine

31st May 2010, 00:08

is there really no factor at all if you are using no wind? ... it doesn't really make sense

One needs to consider what the reason is for the factor .. and that is the variability of wind (component). No guarantees along the way that all will be on the side of the pilot .. just reasonable processes and a bit of statistics. If you need/want to have a bit more fat .. then reduce the quoted headwind a bit (or increase the tailwind).

I have never seen a heavy stop to check the TO data when the QNH drops 1 mb. Is there really no factor in a max RTOW?

No factor, per se, but sensible operators will include a process to give an acceptable level of fat to cover reasonable variations. The effect for a couple of mb is pretty insignificant .. and will be within scatter for the calculated gross weight calculations against which you propose to compare the RTOW data. One needs to keep in mind that the starting point for weight calculations (the empy weight) can be a tad off the mark if you are looking to talk in terms of a few kilos ... lots of traps for young players when it comes to weighing aircraft.

Mad (Flt) Scientist

31st May 2010, 02:08

There is indeed absolutely no pad on the wind if you have reported zero wind; even 1 kt of wind eats into your margins.

But, and this is perhaps what you were asking for, that 1kt of wind does not doom you to the afterlife; it merely eats into the OTHER margins that exist, for things like the assumed level of aircraft performance, or thrust, or braking effectiveness, or ... With a notionally calm wind, it is unlikely that the wind will be grossly in error from that "calm" assumption. So the chances are, unless you are having a really bad day, some other element of conservatism will be there to cover for the wind effect.

john_tullamarine

31st May 2010, 02:25

.. in a nutshell .. there are NO guarantees .. it is all probabalistic.

History suggests that the rules are reasonably OK as we don't have aircraft falling out of the sky day in day out.

What we would like to think we are pushing here is the VERY real need for the pilot to use his perfectly good Mk1 brain (tempered by a bunch of real world experience) when applying the rules as published in SOP type requirements.

The real danger is when the operation becomes blinkered monkey see - monkey do. If you see a reasonable need to insert a bit of conservatism then you should be prepared to do so .. and then argue the toss with the Chief Pilot a day or two later. While we all know of the horror stories associated with "difficult" companies and Chief Pilots .. in the main, most end up being fairly reasonable if the pilot's reasoning is logical and arguable.

aterpster

31st May 2010, 14:20

j_t:
I thought it might be interesting to see how folk fared with some increased difficulty (all in an appropriate, relaxed and friendly manner). The results I found very interesting. Even the more experienced checkies etc., had some difficulty until they'd had a couple of goes to get the gyrations under control.

Thus far you are spoken in generalities, other than to express concern that my splay from the DER to some reasonable RNP linear area would not assure containment because of "rusty pilot" performance.

Specific question: Using FAA's AC 120-91 as a reference, specifically the straight out area method, do you believe your typical "rusty pilot" would not be able to maintain containment from the DER to say 1 mile beyond? ...2 miles? ...or more?

And, what about locations that require a 15-degree banked turn be commenced at as low as 100 feet, afe. (I know of a couple of those in California). Do you feel that a fair percentage of "rusty pilots" would miss the turn requirement or, alternatively, perhaps drop the wing into the dirt?

Is your conclusion that airplanes aren't falling out of the sky is perhaps because engines simply have not failed above V1 (while still on the runway or just after rotation) at critical locations? If so, there is likely no experience in the real world with my example of the turn being mandatory at 100 feet, agl, just after the engine fails.

mutt

31st May 2010, 15:06

OK enlighten us, what product are you trying to sell?

Mutt

aterpster

31st May 2010, 15:52

mutt:
OK enlighten us, what product are you trying to sell?

I presume you are speaking to me.

I don't sell anything other than my flight operations and instrument procedures expertise. I don't design instrument procedures, either; way too much liability. Only Boeing and G.E. have deep enough pockets to do that.

I also don't deal in snake oil, unlike some performance engineering departments I have dealt with.:rolleyes: (present company excepted, of course.)

I also find it incredulous that performance engineering is mostly still in the 1970s as to OEI flight path navigation. VOR systems, as one example, cannot deliver the accuracy presumed by some (many? most?) performance engineering departments. RNAV, and especially RNP, can deliver the goods, so to speak. No marketing concepts there.

john_tullamarine

1st Jun 2010, 03:03

aterpster

First, you have now been identified to me from other PPRuNe sources so I am familiar with your ID and basic background. There is no question here that you are other than very competent in this field so the discussion proceeds on that basis ...

Thus far you are spoken in generalities

Indeed, for other than specific runways the only specifics we can cite are regulatory

would not assure containment because of "rusty pilot" performance

Not quite what I am suggesting.

First, I have no problem with any protected area specification provided that it matches reasonably

(a) the aircraft's equipment capabilities to track within it

(b) the pilot's manipulative capability to do likewise. In this latter matter I have cited only a concern with critical failure cases (and I don't consider the usual proficiency tests as being in any way representative of critical). Personally, my concern is the low weight failure workload. However, the more general problem identified in the old DCA studies still remains valid and, considering the general reduction in manipulative skills in the modern airline world possibly is more a concern these days than in the past ?

Second, my references to concerns about pilot manipulation history is based on competent, current flightcrews - not at all rusty in the general sense.

Using FAA's AC 120-91 as a reference

The answer comes back to the above caveats.

Provided that the recommendations in the AC are observed, I would be confident that a reasonably skilled pilot should be able to address the routine nav tracking requirements. However, my observations in the sim (and the earlier DCA sim studies) indicate that one cannot be as confident for close in OEI situations other than for benign (rather than handling critical) failures.

what about locations that require a 15-degree banked turn be commenced at as low as 100 feet .. would miss the turn requirement or, alternatively, perhaps drop the wing into the dirt?

Not relevant to my concerns and I am not overly concerned about a simple turn situation either AEO or OEI after the failure has been contained. Indeed, my experience is that the averagely competent pilot can readily handle a simple turn with the failure thrown in on top of the navigation workload .. but with the criticality caveat.

is perhaps because engines simply have not failed above V1 (while still on the runway or just after rotation) at critical locations?

While we acknowledge the increased reliability of modern engines, the Standards philosophy still addresses the V1 (or later) OEI situation for the continued takeoff. Therefore, the concern relating to navigation and manipulative reliability remains a concern to be addressed.

I also find it incredulous that performance engineering is mostly still in the 1970s as to OEI flight path navigation.

Putting to one side any constraints which might be imposed by Regulatory pressure, I don't think that either Mutt or I have any problem with reduced protected areas predicated on modern RNAV capabilities.

Indeed, this is getting to be an interesting discussion ..

rudderrudderrat

1st Jun 2010, 09:21

Hi JT,

I don't think that either Mutt or I have any problem with reduced protected areas predicated on modern RNAV capabilities.
Our A319/20s have recently had their Engine Out Strategy changed at Naples RW24. Initially it was very restrictive due obstacles straight ahead on departure, the new OEI strategy is to make an early turn to avoid them and to fly through the "saddle".

The sophisticated RNAV OEI routing is in the secondary flight plan, but this can't be engaged unless the PNF made several key strokes into the FMGC just as the work load peaked. However the "Yellow Track Line" of the OEI is displayed on the MAP which can be followed simply by using the Heading Selection initially.

So it's still down to crew's prioritisation of the tasks and intelligent use of the equipment.

aterpster

1st Jun 2010, 13:56

j_t:
Putting to one side any constraints which might be imposed by Regulatory pressure, I don't think that either Mutt or I have any problem with reduced protected areas predicated on modern RNAV capabilities.

Any reduction would not occur at the DER, rather starting a mile or two beyond the DER. But, that reduction would see the linear containment areas being navigated with performance based navigation instead of a heading or some marginal (at best) VOR radial or NDB bearing.

I can't speak to regulatory requirements elsewhere, but such a modern concept would have no issues with FAA regulations. To the contrary, the path for approval already exists. From what I know, many "first world" nations would have no quarrel using PNB for the OEI flight path. And, some two years ago, Naverus provided just such an OEI flight path for China to use at Lhasa. The Airbus A319 was recently added to that approval:

Naverus | Performance Based Navigation & Required Navigation Performance (http://www.naverus.com/Company/News/2529.htm)

Also from their web site:

RNP AR procedures designed to Naverus’ criteria include:

Instrument approach procedures including missed approaches
Departure procedures
Non-normal (engine inoperative) departure procedures

john_tullamarine

1st Jun 2010, 23:54

the new OEI strategy is to make an early turn to avoid them and to fly through the "saddle".

Generally there are multiple ways to fix the departure problem .. the aim being to end up with a compromise between sensible flight standards and making a dollar by optimising the payload.

this can't be engaged unless the PNF made several key strokes into the FMGC just as the work load peaked.

Crew workload, naturally enough, is part of the flight standards consideration. In my view the desirable option for a difficult runway is to make the AEO and OEI flight paths the same so that the workload is reduced ...

So it's still down to crew's prioritisation of the tasks and intelligent use of the equipment.

That's an operator cop out for something as important as escape procedures. In my view the operator should be prescribing the way the crew is to address the problem. It is quite unreasonable (and leads, potentially, to a significant standardisation problem) to load the crew up with decisions that are not properly in their basket. The crew should be flying it, not planning the escape.

rather starting a mile or two beyond the DER

.. where the 300 ft is overtaken by the expanding splay ..

Non-normal (engine inoperative) departure procedures

This remains the sticking point for me as the question of pilot skill level remains unanswered for the more critical failure cases. The problems associated with the evident skill reduction across the Industry is a bit of a worry if we are going to have the hard bits come in a bit closer to the notional escape path ? .. albeit that the close in areas remain unchanged. In respect to the latter, I think that the sim history suggests some concern anyway.