744 Eng Fail and Vmcg
 

Should you add forward pressure onto the nose wheel with the elevator at V1 (Vmcg =V1) to ensure centreline tracking? No mention of it in any FCTM but in some sims Iv seen you will depart the runway if you don’t.
What I’m really asking is the definition of Vmcg , and does it mean increase pressure on the nose wheel if needed ( as it is Vmcg) and since it’s not written any where , should we be doing it to stay on the runway or re-evaluate our V spds.
Any one else seen this?

Vmcg is defined as the minimum speed, whilst on the ground, that directional control can be maintained, using only aerodynamic controls, with one engine inoperative (critical engine on two engine airplanes) and takeoff power applied on the other engine(s). So where does the nose wheel come in?

The basic requirements for minimum conditions (which appears to be your concern) -

(a) Vmcg can't be less than Vef, rather than V1.

(b) so far as the NW load and NWS is concerned, the certification testing avoids both.

(c) CG max aft and, usually, minimum weight.

(d) XW nil

The problem is that, if you are playing in the real world near Vmcg, generally you aren't going to be replicating the certification requirements so it gets a bit rubbery. Be very aware that the directional control animal gets very aggressive, VERY rapidly, in the last few knots as the speed reduces toward Vmcg - the certification Vmcg flight test stuff potentially is REALLY hazardous.

A significant adverse problem is crosswind. If from the failed side of the house, the "real world Vmcg" (as opposed to the book figure) will go up. This delta can be quite significant and, for a 744, you might be looking at something in excess of 1kt/kt. In the case of a stiff crosswind, a takeoff with a planned min V1 schedule is something which one probably should try and avoid unless the V1 can be increased by an appropriate margin to avoid the XW concerns.

So, the short answer, generally, is that you ought not need to push the stick forward, but it is going to help the situation for the real world pilot, so it fits the bill as a "good idea". Forget centreline tracking ... that just isn't going to happen. I have archived video of some DC9 work we did (TP is a PPRuNer) and, as the runway head cameraman, it was quite illustrative to see just how the DC9 (said by just about every DC9 pilot to be an aircraft on rails with a failure) promptly leaped out of the viewfinder ... except for the wingtip. The aircraft will yaw, deviate and then, if things go well, either parallel or, maybe, come back towards the centreline a tad, prior to lift off. There is no specific requirement for either of these to occur and one could well see the deviation limited by the liftoff. Generally, the continued takeoff is the critical situation as, in a reject case, the throttles will be closed in short order.

Have a read of the flight test things at page 111 of AC 25-7C Flight Test Guide For Certification Of Transport Category Airplanes (faa.gov)

The current rulebook requirement is at FAR 25.149(e) - see Electronic Code of Federal Regulations (eCFR)

You would need to do some homework to see if the 744 met these requirements or something earlier and, perhaps, a little different. I'll leave that for your spare time ...

flyhigh55,
Alway use the procedures in the manufacturers FCOM.
Do not invent new techniques just to fly the simulator; simulators are good, but they are not the real aircraft.
Check the procedure being used, check the simulated runway conditions; all else being equal on a dry runway it should be possible to limit the centreline deviation to 30ft with prompt application of full rudder.

N.B. Forward stick in some aircraft can reduce main-wheel loading, if so, tendency to go sideways !

V1 is always greater than Vmcg
"Understanding Takeoff Speeds"
https://skybrary.aero/bookshelf/books/493.pdf

Airbus “Getting to Grips with Aircraft Performance"
https://www.skybrary.aero/bookshelf/books/2263.pdf

No! The nose-wheel steering is likely disconnected at this point (don't know how it works on the 747) and it's definitely not designed to have the lever moment generated by the elevator at high speeds loaded onto it.

Good discussion. But as suggested above, there are no mandatory rules that govern the pilot's need for action under this condition. It's considered a remote surprise to the pilot requiring different judgements.
e.g.. imagine the condition where an engine goes to unwanted max power on one side at this speed condition. That will take several seconds to sort out

vilas- on the the 744 you would see that you do get better center-line tracking at Vmcg if you add pressure to the nose wheel using " aerodynamic forces- (elevator)" {not NWS)

Thank you John tullamarine. It is that gray area where X-Wind comes in that I have experienced the issues. definitely something to be aware of even if we are talking about a very small window.

No! The nose-wheel steering is likely disconnected at this point (don't know how it works on the 747)

Now, that's something I haven't come across before. While the FT folk might do their tests with NWS physically disconnected to tick the certification box, the idea of such happening out there on the line is a new one. Are you able to add some commentary as to any Types which might do such things, etc ?

it's definitely not designed to have the lever moment generated by the elevator at high speeds loaded onto it.

Likewise, might you be able to provide some evidence to support this contention ?

on the the 744 you would see that you do get better center-line tracking at Vmcg

That probably will be the case for the great majority of aircraft - anything which gives you some cornering forces is going to help. However, it is pertinent to keep very much in mind that the aircraft is going to diverge, regardless. Considering those test chart results I have seen, this applies even at high speed as there is always going to be bit of a delay before the pilot gets the rudder in and the aircraft responds. Generally, you are going to see a small deviation which starts to increase as you get back closer to Vmcg and then things really ramp up and get hairy in the last few knots.

It is that gray area where X-Wind comes in

I'd be a little more concerned than you, I suspect.

First, if there is much crosswind, all certification bets are off. Keep in mind that things like Vmcg are just lines in the sand for other certification activities. The pilot might not need to have a detailed certification knowledge but it sure helps to have an idea of which bits, and where, can bite you ... and badly.

The usual test requirement is nil wind. The old BCARs used 7 kt but we can discard that as being in the dinosaur realm. Consider that your four-motored beast might see something in the order of a, perhaps, 20-30 kt increase in the real world Vmcg with a stiff crosswind. That is to say, even allowing for the other conservatisms, you might find yourself considerably BELOW the real world on the day Vmcg but perfectly legal with your min speed schedule takeoff. The only problem is that, should a critical failure occur on the wrong side of the house, and you elect to continue, you ARE out of control and you WILL go for some tip-toeing through the tulips. In such a situation, V1 becomes irrelevant and the only option is a (slightly) above V1 reject.

Better, if you have the option, just to avoid the potential problem altogether. For example, the situation could well arise for an empty positioning flight from a long runway. If your laptop or RTOW book uses min speeds, then you would have the option to presume a higher weight and take advantage of the relevant higher weight speed schedule. We are just trying to get a suitable buffer to take us out of the nasty region.

Going back many years, I did a training contract on the 732. The operator had a routine positioning flight where this was absolutely relevant (and, often, windy). Once it became apparent that the folk had not thought much about this concern, some directed training quickly and clearly highlighted the problem and a suitable solution. Some of the wide eyed exercises were a delight to behold.

Although certification is pretty good and looks after us pretty well, that only applies most of time. Sometimes we need to read between the lines a tad.

Betwixt theory and practice, 'what-if', 'except', … reality.
 

Realism, an operational view.
NWS, fwd stick are theory, consideration of which risks creating inappropriate procedures, bad habits, biased mindset.

The practical rules are:-
#1 fly the aircraft as defined in the manual, as practiced.
Note that scenarios posed in debate are fixed, rarely like reality.
Adding distraction from a bang, vibration, fire bell, surprise, all consume mental ability - no 'what-if'. The minimum standard is to recall and fly the essential basics.
If you are at V1 you are going to fly; don't play with the stick, you will need to act at 'rotate' with back stick; how much, how different from the norm - recall training - can you describe it.

At V1 and above you GO; no redefinition of parameters or consideration of rarer 'except' situations. JT we need a word in the naughty corner; theory vs practice.

Crosswind, wet runways are real. Certification provides some margin - 30 ft and a second or two in dry conditions. In real-world adverse conditions the margins may be exceeded, using all runway width (how wide), even some of the grass; the piloting task is to fly as accurately as possible, avoid mishandling which could add deviation.

The 'what ifs' of these situations must be considered at pre flight briefing; a slippery runway, crosswind, and 'up north' snow banks, soft muddy ground.

Failures rarely occur at the critical point, but because of 'Sod' the worst case is practiced. Time doesn't stop as in debate or simulation, the aircraft will continue to accelerate, rudder increasingly effective, lateral excursions can be reduced.
Attention switches to getting airborne, and at lift off further 'surprise' from the forgotten crosswind - aircraft yaws, going sideways again.

Then how to avoid the obstacle which looks very close, fly V2; more distraction with increasing altitude - EGPWS (active >50 ft) sensing height over the real terrain (not in simulators), 'Don't Sink' - but you are already doing your best …

… and thats only the start of rule #1.

we need a word in the naughty corner; theory vs practice

Indeed.

My driving concern, though, is to have folks think about things in their armchairs over a port and at planning. For winds, if the crosswind is brisk and we might be inadvertently put into an unfortunate min schedule situation, can we mitigate the problem in advance so that the worry factor goes away ?

In the general situation what we train for is what we should do. Very rarely, though, circumstances conspire to defeat the theory game plan and we may need to be innovative to survive. Most of us aren't called upon to make those sorts of calls throughout our careers and, on the odd occasion, it just doesn't warrant getting out of bed in the morning.

Hi John,

The aircraft types I've flown (Airbus narrowbody, Boeing 787) both bleed out NWS orders from the rudder pedals as ground-speed increases. That's what I was implying when I said disconnected. My apologies, I could have made it clearer.

It's a moot point in my opinion because V1 is always greater than Vmcg, so if you can't control the aircraft with the nose wheels on the ground, you're going to face exactly the same difficulty during rotation.

Thinking it through, you're absolutely right. I suppose the elevator can only just overcome the weight of the aircraft on the nosewheel during rotation, and authority in the nose-down direction is probably less. Given the way the 787 falls onto its nose wheels during derotation it must be a non-event.

I don't know whether the elevator could generate sufficient force to wheelbarrow the aircraft onto the nose gear.

JT, I share your concern. :ok:
Tech Log is a very valuable resource; however the line between theory and practice is blurred, and quite often assumes that contributing posters have the same understanding.

Pilots need theory, but also and more important, how this is should be applied, the limits and assumptions in certification, and to consider the practical aspects, not least the self generated biases in risk assessment.

In our very safe industry there is increasing risk of self inflicted problems from weak understanding of the application of theory in practice. Humans like to consider the what-if situations, how to be a hero, save the day with innovative knowledge and procedure, whereas there would be greater benefit considering the 'everyday' situations which can be managed - before the event, avoided, mitigated (as below).

A testy, cold, snowy, and locked-down new year, dreaming of a sunbaked barbie (with port). Also the lack of the favourite Ozzy Red, replaced by an African white titled The Weatherman !

Situations involving lateral excursion which can be avoided.
https://safetyfirst.airbus.com/engin...ng-at-takeoff/

The aircraft types I've flown

Many thanks for that, good sir; yet, again, my knowledge base increases daily. I might speculate that the reason is associated with no need for NWS at higher speeds ?

It's a moot point in my opinion because V1 is always greater than Vmcg

And that is the basis of certification's trying to keep us out of harm's way by so arranging. Just that niggly real world crosswind problem which gives me some heart flutters at times.

I don't know whether the elevator could generate sufficient force to wheelbarrow the aircraft onto the nose gear.

Certainly some can but not the sort of thing one aims to do ( ... unless you fancy displays in Caribous - DHC caribou doing the "wheelbarrow" - YouTube - not quite the same thing but was always impressive to watch)

you're going to face exactly the same difficulty during rotation.

Although the extra speed might just be your saving grace.

I agree with safetypee:
Inventing novel new techniques because you ‘know better’ than the manufacturer/operator/regulator leaves you very vulnerable, and not just in a legal sense.

For an engine failure after V1, the appropriate amount of rudder must be used to keep the aircraft ‘straight’ as the take off continues. If full rudder is insufficient to achieve that, how much should we then push the yoke forward? A bit? A lot? Full forward? Just before hauling the yoke all the way back to rotate? Sounds challenging to me.

That’s before we even consider the fact that we are going to be rolling down the runway at speeds well in excess of 100mph. We then load up two inflatable rubber tyres with a number of tonnes of aircraft mass and aerodynamic loading whilst they are not facing in the direction of travel?

Whilst this may not be modelled correctly in any simulator, (why on earth would it be?) I can reasonably imagine a likely outcome of the coefficient of friction in a ‘real world’ event could easily be two burst nosewheel tyres, before any noticeable turning moment occurs. Then what?

I’d prefer to be taught such novel techniques only after a test pilot (preferably the manufacturer’s!) has proved it’s a good idea. Rather than just because some bright spark thought it was a wizard wheeze!

however the line between theory and practice is blurred

Therein lies a major philosophical problem for us: what to do ? Do we dumb it down to the lowest common denominator and the whole thing becomes a PacMan game, only with real world hazard potential ? or do we throw out some information and robust discussion with a hope that most of the folks will contemplate such in the vein it is intended ?

Pilots need theory, but also and more important, how this is should be applied

Is not that paragraph the underlying crux of the whole educational problem ?

replaced by an African white

.. which brings to mind a delightful drop (Amarula) with which I became intimately acquainted during a SAA training contract long ago. Nectar of the Gods. Fortunately, it is imported to Oz so the affair can be maintained.

Hopefully folks will read and reflect on the Airbus note.

Inventing novel new techniques

I see no evidence of such in the thread. However, some reflection upon reality probably is of use to line folks.

From the very first lines of this thread:
”No mention of it in any FCTM”

Sounds a pretty ‘novel’ technique to me.

That's a thought to consider.

Hopefully there is some confidence from discussing stuff like in a tech thread to reduce the surprised factor when faced with an unfamiliar combination. The larger danger, however is to substitute such in place of what the manufactures have recommended.

The manufacturers spend lot's of time pouring over pilot incident reports to understand what works and how often. Of course they don't see the really rare stuff except one or two in ten years in a single design fleet.. The one thing that bothers me is listening to CVRs where pilots run out of options with words like "it's gotta work"

I don't remember anything about nosewheel steering becoming disconnected from rudder pedal input on the 747. That was on the Airbus if I remember correctly......at least the narrowbodies.

Even if the nosewheel does become disconnected on an aircraft type, it doesn't mean that more downward pressure on the nose won't help for directional stability(just like aft elevator helps for directional stability in the 3 point attitude on taildraggers). And, as I have discussed with John before(under a different handle of JammedStab), there is no consideration for crosswind in VMCG calculations, meaning actual VMCG can be much greater or much less than what would be published. It is one of those dirty little secrets that almost training organization/manual/etc never talks about. Then you get a surprise one off accident like the American Airlines A300 in NYC(where we discovered that Va is different than what many people thought it was) and word gets out.

There is also no mention in the FCTM that VMCG is invalid as soon as there is a crosswind. Even when we did one engine inoperative takeoff training in the sim on another 4 engine type I flew, no mention was ever made of the effect on crosswind for a situation where it really does have huge real world consideration for that takeoff. The winds were always calm for that scenario.

I gave the definition. Should you be increasing pressure on NW? Do so if it pleases you. . Manufacturer does tell you about crosswind takeoff/landing, EFTO and many other handling techniques. If he doesn't say it then it couldn't be making much difference. Calculation of Vspeeds? EFB does take more than half a dozen things in consideration while calculating. Airbus does progressively reduce the authority of NW steering to zero as speed increases. Airbus safety first magazine issue 11 tells you about minimum Control speed tests of A380.

tcasblue: This discusion is about the rare occasions when the V1 is low enough to equal Vmcg. In most cases there will be a split between the Vmcg and the higher V1 so any engine failure requires the thrust be reduced to abort and therefore the handling issue goes away. I did once have an engine failure on take-off in an A340 well below Vmcg and the swing initially was very great and took us off the centreline before the thrust was reduced.

From the very first lines of this thread:

Fair comment. Two ways to view the thought. Most OEMs of my reading recommend a forward stick load for takeoff in a crosswind (often with a suggestion to wash the load out as the speed increases) so an "increased" NW load of whatever magnitude is there at the failure. Concur that I can't recall a suggestion to increase loading post failure for the continued case. My take is that the line pilot, typically, has more than enough to keep him/her busy without worrying about an additional stick load input. However, the point stills remains that the thrust of the thread is background discussion to encourage thinking, rather than overt suggestions to encourage novel handling techniques.

Hopefully there is some confidence from discussing stuff like in a tech thread to reduce the surprised factor when faced with an unfamiliar combination

Therein lies a prime value of this Forum.

The larger danger, however is to substitute such in place of what the manufactures have recommended.

This is a critically important consideration. In respect of emergencies, etc., the OEM, generally, will have the preferred story for the line pilot.

meaning actual VMCG can be much greater or much less than what would be published

Hence the concern when the line pilot is faced with a min speed schedule which may put the operation somewhere near the real world, on the day, "Vmcg" (as opposed to the fixed book figure). The danger is that the typical pilot has little/no exposure to the nature of Vmcg and just how savagely handling can change in that speed region during a takeoff failure. A bit of the old forewarned is forearmed; the preference is to avoid having one's first exposure to a particular class of excitement on the fly, as it were.

Even when we did one engine inoperative takeoff training in the sim

Which is why some of us made a point of exposing newbies in the sim (even if the box is not altogether tops in fidelity) to such things for the exposure/discussion/thinking in the armchair value

Didn’t see it mentioned above but the 744 FCOM and FCTM state that forward pressure should be applied from the start of the takeoff roll and gradually released so neutral is achieved by 80 knots IAS.

Meikleour What series of A340 did you have the failure in ? When I first flew the A340-600 I was surprised how high the min V1 was around 141 Knts from memory, having come from a 300 series with again from memory a min V1 of around 124 knots. Whenever I was in the 600 I mentally questioned the Airbus go mindedness 100 knot philosophy when it was so far below the minV1 which I guess was a Vmcg limitation.

There is a possibility that omission is due to the fact that some here have no experience on the 747-400? Or the dubious effectiveness of it’s nose wheel? Certainly when compared to the power of it’s rudder.

If we’re talking about ‘real world’ situations, the very last thing I wish to be discussing with a colleague (even in advance of any potential event) is the notion of attempting something totally non standard picked up after reading an internet forum. Where some bright spark thought it was a wizard wheeze!

If it’s considered ‘best practice’ then ‘our people’ should get in touch with ‘their people’ (the manufacturer) and get it written in the manuals!

Anything else is well off piste.

Out of here: I have just looked at my old manuals and for the -300 Vmcg was 126.5kts (-600 Vmcg was 136.5kts ) My incident was on a -300 TOGA departure.

With a min V1 driven by Vmcg it is hard to see a situation where TOGA is being used therefore the handling issue should be less critical in practice since less than TOGA thrust is usually being used. That is the very reason why Airbus certify Derated Take-off Performance to allow slippery runway ops with low V1s.

I do not think that Airbus are talking about engine failure when they talk about being "go minded" above 100kts.

Meikleor: Thanks very much, sure I get the 100kts thing is just an arbitrary number not intended for engine failure more a kinetic energy V squared thing for other failures. When operating both types I was very aware of the performance differences and as JT has mentioned I think it is good practice to sit in the armchair/bath/bar and think these things through. Interestingly my operator at the time did not utilise De-Rated power just Flex up to isa+60 (600) ie max flex 75 at sea level corresponding to a 40% power reduction. I don’t suppose you remember roughly what speed you had your failure at in the 300?

Definitely not! Being Go minded is not a blanket clearance to just carry on. FCTM specifically mentions five categories of failures which call for reject takeoff even after 100kts. The second category is sudden loss of thrust also in the fifth category it gives five failures for which to reject the second is engine failure. To be go minded the aircraft must be controllable. A320 VMCG is 109kts and beyond.

I sure don't understand this. So many accidents due to aborts at 100+ kts on the big iron and so few cases where the situation was seriously in doubt to justify abort above 100 kts. Sure the pilot must make a decision based on his perceptions, but I do think that it's unwise to issue a blanket piece of advice of when to go and not to go

The reasoning for the advice to be 'biased' as 'go' minded at high speeds stemmed from the TakeOff Training Safety Guide.
Perceptions are subject to error; knowing beyond reasonable doubt grows with training and experience (hopefully always in the simulator).

A simplified view:-
https://www.flightsafetyaustralia.co...0/think-quick/
for info:-
https://flightsafety.org/files/RERR/...gSafetyAid.pdf

https://www.skybrary.aero/bookshelf/books/921.pdf

https://www.skybrary.aero/bookshelf/books/197.pdf

https://www.skybrary.aero/index.php/...off_(OGHFA_SE))

https://www.skybrary.aero/bookshelf/books/1326.pdf

Out Of Here: Sorry, it was a long time ago - it was certainly before the 100kts call which we also used as an ASI confidence check and therefore my view was outside at the time! An interesting sidestory about this was although it was the failure of some turbine blades out the back of the engine which resulted in a massive engine surge and an EGT in excess of 1,000C - when we came to a halt there was NO appropriate ECAM displayed!! This initially flumoxed the F/O since it was his first line trip and he never had thought that he might have to do the ECAM items from memory! Perhaps the differences in Vmcg may have been because of different engine ratings?

Meikleour: A very interesting experience, thanks for sharing. On the first sector side of things I once had a reverser partially deploy on a 340 at rotate, it turned out to be a primary lock failure but the secondary caught it.
Again it was the F/O’s very first line sector albeit a short one! Apologies for thread drift.

From Airbus Safety First:

• What are the operational implications of not respecting V1?

Supposedly, there are two different ways of “disrespecting” the V1 speed criteria:

1 - The crew decides to continue take-off while an engine failure occurred before V1.

Standard procedures encourage the crew to reject take-off if an engine fails before V1. If take-off is continued despite this recommendation, then the aircraft can potentially exit the runway laterally, or be unable to take-off before the end of the runway.

2 - An RTO is initiated above V1.

Virtually, any take-off can be “successfully” rejected, on the proviso that the reject is initiated early enough and is conducted properly. In this respect, the crew must always be prepared to make a GO/ NO GO decision prior to the aircraft reaching V1.

Doing otherwise exposes the aircraft to an unsafe situation where there either may not be enough runway left to successfully stop the aircraft - therefore resulting in a longitudinal runway excursion-, or maximum brake energy is exceeded and brakes catch fire.

Thank you very much, now may we have a B747 procedure covering the same situations?

Recollections of the B744.

One of the company's 744s at a slowish speed (well below 80kts), but at max power, rapidly lost the power of one of the outboards. As the aircraft swung violently into the dead engine, the crew in quicktime idled the throttles, stood on the brakes and pushed hard on the nose wheel steering in the opposite direction. Stopped 3 feet from the grass only because of the instant response from the crew.
So, until 80kts when the rudder has some control over direction, we kept a slight nose down pressure on the stick to keep the nose wheel reasonably firm on the ground, and of course, if required a little into-wind aileron.
Personal technique: Most of my experience with the 744 was either long haul or ultra long haul, therefore trundling down the runway, with the speed increasing towards V1, thoughts of abort are always present. However, as the speed approaches V1 (eventually), about 5kts prior, I used to uncurl my fingers slowly from around the throttles and move my thumb away from the disconnect. Hand still in contact with the top of the throttles until V1, them fully smoothly remove. WE GO FLY?? Not quite yet, as a few more long seconds are required until rotate, and then select the attitude, and hopefully claw into the lower atmosphere!!

Low speed reject requires simultaneous application of full rudder, differential braking and thrust reduction all the way into reverse(at least on Airbus twins) which turns the aircraft away from the failed side. Those who takeoff with feet up on the rudder peddles and use the steer with heel and brake with tow technique find it easy to control the swing. Those who takeoff with heels on ground may struggle to get the foot up for differential braking. In 747 classic the nose wheel is not connected to the rudders and in the simulator this exercise with runway wet was challenging but still it was manageable if feet were up.

(airbus twin hijack) More specifically into the grass towards the failed side. The FCTM explains the proper sequence. (/hijack)

[* vilas quoting the OEM guidance non-explicitly? Welcome 2021, until today and I thought the previous was the bad one. Not even a full week, fluff!]

Thank you for correcting. Actually away from failed side. Corrected the previous post also. Getting rusty, though just had a LVO sim session.

This again,

Are there any operators out there who encourage this dubious practice ?

Heels should be on the floor for take off and on landing until initiating manual braking