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.

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.

We don't avoid the regulations:

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 think that you have to look at NET and GROSS gradients.

We analyze 900 meters either side!

Are you talking about a particular aircraft type?

Mutt

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.

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.

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.

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:

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

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 ....

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

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

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 ...

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.

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".

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).

Hi Mutt,

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.

John Tullamarine:
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.

galaxy flyer:
.

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.

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?

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.

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.

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.'

J_T and Mutt

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

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!

mutt:
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.

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.

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.)

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.

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


Mutt

What's that ?:)

mutt:
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.

Don't know those acronyms. :)

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.)

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.

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.

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.

j t:

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.

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 ?

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!

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)

Thank you:ok:

Turn after T/O - One Engine Inop.
 

FCTM 737 :

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

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.

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...

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.

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.

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.

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.

j_t:
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.)

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.

j_t:
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.