Limiting Factors For Takeoff

[aterpster]

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]

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]

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]

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]

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]

Originally Posted by johns7022

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]

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.

[galaxy flyer]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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

GF

Firmly resisting any excursions in Vmcg discussions!