Thrust selection after engine failure/ fire on takeoff

[John Citizen]

As I understand there is no requirement to select max. thrust following an engine failure on takeoff using reduced/flex thrust.

However I have come across many different opinions :
- some say always immediately select max. thrust to improve climb performance
- some say leave the thrust as it is, to avoid destabilising the aircraft, and then perhaps add aditional thrust (if required) once the autopilot is on

I suppose these are all acceptable techniques, however some also say :
- don't ever increase thrust if an engine fire (don't add fuel to the fire)
whilst others say
- it's ok to increase thrust (on both engines) even if an engine fire

I have looked through the manuals and can not find any specific instruction regarding the selection of max. thrust following an engine fire.

With so many opinions and techniques out there, it gets a bit confusing what to do. Everytime I am in the sim. I come across different techniques and I am always having to retrain myself. But seems like no matter what I do, some checkie will come up with a different technique yet again. Just can't win sometimes :{

I am interested in hearing other peoples opinions.

[punk666]

The assume/flex take off takes into consideration of an engine failure and its climb performance.

So there is no need to add additional thrust in the event of an engine failure after takeoff unless you really need!!

In a turbo prob maybe this might be the case because the dead engine will produce alot of drag and props are not as powerful as a turbine engine.

But from a jet point of view with an engine failue you rotate at a slower rate and pitch attitude usually around 12.5 degrees (B737).

Assuming your maintaining runway heading, at your designated accel altitude you select flaps up speed and accelerate selecting the flaps up on schedule. Once the flaps are up and your still climbing you would ask for level change (B737) and ask for max continuous thrust.

Thats the way I have been taught, some suggest getting the autopilot in straight away to reduce workload, some say dont bother till level flight so you can trim the aircraft easily instead if doing it during a climb and constantly re-trimming as you speed up.

[Spendid Cruiser]

Here is the 737 FCTM extract:

Engine Failure During a Reduced Thrust (ATM) Takeoff

Since the reduced thrust (ATM) takeoff must still comply with all regulatory takeoff performance requirements, it is not necessary to increase thrust beyond the reduced level on the operating engine in the event of an engine failure. However, if more thrust is needed during an ATM takeoff, thrust on the operating engine may be increased to full rated takeoff thrust by manually advancing the thrust lever. This is because the takeoff speeds consider VMCG and VMCA at the full rated takeoff thrust.

Increasing thrust on the operating engine to full rated takeoff thrust provides additional performance margin. This additional performance margin is not a requirement for the reduced thrust takeoff and its use is at the discretion of the flight crew


Messing around with thrust is an additional task in a demanding and critical
situation and yet adding thrust would increase your rate of terrain separation.

My view is that one should dispense with rigid solutions and simply remain situationally aware and assess the risks, remain flexible and attempt to go with the least risk option by balancing sensible precautions with workload according to the conditions.

Sometimes you just have to agree to disagree. Personally, I endeavour not to be railroaded by examiners, instructors and Captains (or any other more experience pilot). I don't know what your experience level is, but I found that the confidence required to politely push back on advice that lacks merit, especially during a recurrent sim, takes time to develop.

[john_tullamarine]

Summary of some points to keep in mind -

(a) derate/flex meet the certification requirements - then why do we accept going at MTOW in critical conditions ? Double standard ? The days of pilots doing things to make life more comfortable for pilots during flight have long gone to make way for LoCo competition.

(b) derate is the limit so there is no increase beyond that during the takeoff phase

(c) flex can be run up to rated/derated as applicable

(d) if (c) is applied, be VERY wary of dynamic effects on thrust and subsequent yawing moments. I was involved in the investigation of one fatal where this was very likely a contributing factor.

(e) if (c) is applied to a turboprop, be careful of drag effects due to prop blade gyrations - similar concern to doing asy work by snap closure of the throttle - one can get significant drag on the "failed" prop

... as GF observes in a parallel thread, do it slowly ...

[John Citizen]

extract from the Airbus Flight Crew Training manual :

THRUST CONSIDERATIONS
Consider the use of TOGA thrust, keeping in mind the following:
• For a FLEX takeoff, selecting the operating engine to TOGA provides additional performance margin but is not a requirement of the reduced thrust takeoff certification. The application of TOGA will very quickly supply a large thrust increase but this comes with a significant increase in yawing moment and an increased pitch rate. The selection of TOGA restores thrust margins but it may be at the expense of increased workload in aircraft handling.

[aterpster]

John Tullamarine:

(a) derate/flex meet the certification requirements - then why do we accept going at MTOW in critical conditions ? Double standard ? The days of pilots doing things to make life more comfortable for pilots during flight have long gone to make way for LoCo competition.

True, but a lot of rote there.

If departing an Aspen or an Eagle, just forget derate/flex thrust completely. The price of being wrong if nothing happens is very low. The price of being wrong if you select derate/flex thrust at such locations, particularly during unstable atmospherhic conditions may carry a very high price for being wrong.

[390cruise]

Guys

Most pilots will not experience an engine failure during a career of thirty or fourty years.So are we saying that as we climb away after the event we are happy with less than 50% thrust even though we have increased drag from control deflections (and perhaps damage) ? Aimanship??

Reduced thrust is based on takeoff mass as shown on the load sheet.Load sheets are based on standard masses of humans and bags. During my B737 and A320 years I think the actual aircraft mass was often two or three tonnes higher than shown.

The manuals, company, flight crew training, etc etc vary and change.....so what do the people who build the aircraft think?

The Airbus 'Approved flight manual' (remember when these were carried onboard?) has limitations for use of reduced thrust. One of these is........when an engine fails during a reduced thrust departure TOGA shall be selected on the operating engine.

So engine failure, smooth selection of TOGA, trim then autopilot.

390

[SNS3Guppy]

However I have come across many different opinions :
- some say always immediately select max. thrust to improve climb performance
- some say leave the thrust as it is, to avoid destabilising the aircraft, and then perhaps add aditional thrust (if required) once the autopilot is on

I suppose these are all acceptable techniques, however some also say :
- don't ever increase thrust if an engine fire (don't add fuel to the fire)
whilst others say
- it's ok to increase thrust (on both engines) even if an engine fire

John, you may be confusing different events or scenarios.

Given a power loss, engine fire, failure, or other problem after V1, in which the airplane is still going flying (given that insufficient room remains to reject the takeoff), one is going to continue using the thrust with which the takeoff has been planned, and briefed.

A reduced thrust takeoff, as others have noted, takes into account performance with an engine loss. The speeds that are calculated are crafted with this in mind, and the performance that remains with an engine lost. The rejection numbers are applied accordingly. Add thrust, and one may very well have a dangerous condition, especially at low speeds during the initial takeoff. The best course of action is to leave everything alone, climb to a minimum safe height, begin to clean up...and during that time one can apply maximum continuous thrust, run checklists, etc.

If one has an engine fire on takeoff without any thrust loss, why on earth would one want to increase thrust or need to do so? That makes no sense.

If an engine fire occurs during the takeoff at a point where stopping is no longer an option, then the same procedure occurs. Climb, get to a safe altitude to configure and run checklists, then handle the emergency. Unless actual control of the aircraft is threatened, then one has a singular priority during the takeoff; maintain control of the airplane, and fly it to a safe altitude. Only after that has been accomplished does one begin changing airplane configuration, power settings, or addressing the emergency.

As always, fly the airplane first.

[390cruise]

SNS3Guppy

'one is going to continue using the thrust with which takeoff has been planned, and briefed.'

Indeed......my brief will include 'in the event of an engine failure after V1 I will select TOGA'.

I accept your comment about selection of high power on one engine at low speed but have not found it to be limiting.

The engine fire case 100% agree with you.

We should all remember that it is very important to comply with the approved standard operating procedures of the aircraft operator.

390

[John Citizen]

John, you may be confusing different events or scenarios

I am talking about engine failure after V1
- with/without a fire

[SNS3Guppy]

I know you are, John, but your responses indicate some confusion all the same.

A takeoff based on reduced thrust is predicated on keeping that reduced thrust setting; the performance, takeoff distance, and climb performance that are predicted as part of the pre-takeoff calculations are based on continuing the takeoff with reduced thrust.

Certainly if one finds one's self in a situation requiring greater thrust, it may be increased. However, one may also find one's self in a position of having insufficient control authority if one has used the performance numbers for the reduced thrust takeoff.

Remember that increasing thrust asymmetrically increases yawing moment. One needs a certain amount of rudder (and aileron and spoiler deflection in many cases) to counter this increase. At low speeds, pushing power on the good engine may counterproductive. The takeoff has been planned to safely continue, and meet all the applicable climb requirements, with the existing reduced thrust.

Whether one is on fire or not, or whether one has a fire indication, doesn't change the basic requirement to fly the airplane. Unless the procedure for your particular airplane calls for increasing thrust early in the takeoff, then one should not do so. Whether the airplane is on fire or not doesn't change that requirement: fly the airplane to a safe altitude, clean it up, and handle the abnormality or emergency.

If a fire warning occurs, silence the warning, continue, clean up, and execute the memory items or checklist items as appropriate. The rules don't change: Aviate (fly the airplane), Navigate (direct the airplane), and Communicate (talk about the airplane). Do that.

If you're on fire, remaining airborne for an extended period isn't in your best interest. Fly the airplane, first and foremost. If you've lost thrust and have an engine-out (and burning), then you've got the same problem initially as with a simple engine failure. You're going to fly the airplane to a safe altitude, begin speeding up and cleaning up, address the problem, fly the turn procedure or navigate otherwise as required, and notify ATC or other resources as necessary. If you're on fire, you'lll be likely returning to the airport very shortly. In order to do that, you need to fly the airplane.

Your question asks about an engine fire, and increasing thrust on the burning engine. Clearly, if one isn't going to increase thrust with an engine failure, then one isn't going to increase thrust with an engine fire.

Our procedure in the event of a power loss during takeoff, after V1, involves climbing to a pre-determined minimum level-off altitude, and stopping the climb. We begin cleaning up the airplane, and with the initial increment of flap retraction, we set max continuous thrust. We then clean up the airplane, address the problem, run the appropriate checklists, and in the meanwhile navigate as necessary while requesting help.

What we don't do is increase thrust. Reduced trust takeoffs are constructed with a power loss in mind. It's already taken into account insofar as runway takeoff distance required, and the climb performance once airborne. It's also predicated on other factors, each of which combine to either make it safe to do the takeoff with an engine failure at or after V1, or not. If not, then it's not a reduced thrust takeoff. If it is safe, then a thrust increase isn't required.

If you happen to fly an aircraft that uses a different protocol, then follow that.

[Exaviator]

Anyone who has been through the Airbus training school at Toulouse will be familiar with two standard answers from the instructors there. The first being,"It is automatic". The second being, "You are the captain, it is up to you".

The latter is applicable in this discussion. Performance calculations dictate that you do not need to apply extra thrust following an engine failure, BUT hey if you need it, TAKE IT, all the way to the firewall if necessary.

That's why you get paid the big bucks - to make decisions and take responsibility for them. Or at least you did in my day, has any thing changed???

[Escape Path]

If one has an engine fire on takeoff without any thrust loss, why on earth would one want to increase thrust or need to do so? That makes no sense.

As one wouldn't immediately reduce power on the smoking engine either despite the fire bell. It is giving some thrust output, use it in the initial climb. Once you are a bit a away from the tree tops and with the gear and flaps up, then you can shut down the engine completely.

Or so I was taught... :}

Escape Path

[stilton]

Unless performance is not working out as planned after an engine failure I would always leave the thrust alone.



On the 757 in particular there's a fairly healthy yaw into the failed engine, once youv'e got that sorted out why b****r around with your controllability again by adding power.



More Importantly, you only have one engine left and you might want to take as good care of it as you can until you have landed :E

[firefish]

Having not flown any aircraft approved for any kind of derated thrust during take off I can still agree on that it might be wise not to change the configuration of the aircraft as well as treating the remaining engine with a little extra care.

But on the other hand the engines are certified and approved for running at t/o thrust for a certain time (in my case 10 mins when single engine - this might be the common rule) meaning that there really shouldn't be anything to worry about. In addition to this one must also consider the reason for say an engine failure and depending on the conclusion drawn it may very well be a good idea to set max thrust on the remaining engine in order to get as far from the ground as possible before the it quits too (fuel filter by pass on the running engine - contaminated fuel).

What it all boils down to - as usual - is that it is up to the captain/crew depending on the specific conditions for every specific scenario. It is impossible to say that either of the procedures is always right (or always wrong). I can recall a number of accidents where aircraft have been lost, both due to the crew not selecting max thrust when needed to and in some cases when they have killed the remaining engine by doing it.

As always, fly the aircraft and don't just do stuff without thinking first. Even though a V1 cut is about as bad as it can get it's what we all have been trained for and what the airplane has been built to do (with some safety margins too) and it's not about split second decisions. I absolutely agree on that you should engage a/p asap, if the conditions permit, in order to free capacity so that both crew members can start to evaluate the situation properly.

[john_tullamarine]

If departing an Aspen or an Eagle, just forget derate/flex thrust completely

Absolutely the case that some circumstances dictate the use of rated thrust. As a wise checkie once counselled me "Lad, read the Ops Manual with a modicum of commonsense"

Likewise I have never inclined to the view that one should make a non-limiting takeoff into one by, for instance, flexing to the limit. For that reason I always liked Wal Stack's approach when he introduced flex to Qantas - leave a pad for mum and the kids in the calculations .. that also made the new procedure a lot easier to market to flightcrews.

I have no inherent problem with running up the operating lever a bit. Only three caveats -

(a) know where you are with respect to Vmc

(b) do it ever so measured and steadily

(c) have some practice exposure to the exercise in the sim prior to chancing it in anger ....

[FullWings]

As always, fly the aircraft and don't just do stuff without thinking first.
Absolutely. There are not that many of what some call "time critical scenarios" and only a handful of those need *immediate* pilot input, such as RTOs and hard GPWS warnings.

On my first jet (737-200), the company SOP was TOGA thrust on the live engine after engine failure. We then started operating FMC-equipped variants (300/400, etc.) and had done so for quite a while when someone new to the fleet pointed out that this was not such a good idea as at high derates and low weights, as you could end up very close to, even possibly at or below Vmca, due to the way we calculated the speeds. Cue overnight new SOPs.

Engine "fire" warnings: all they tell you is that somewhere in the nacelle, the temperature is high enough to have triggered the detection system (or there's a fault in the wiring). It doesn't often mean that flames are gushing from every orifice and the engine and/or wing are about to burn off, although this is a possibility. Unthinking and/or panicky reactions to warnings can often put the flight in substantially greater jeopardy than a more considered approach...

[MD83FO]

one of the most compelling reasons not to increase thrust that I learned from early jet aircraft literature, is that the more thrust you demand from an engine, the higher the chances of it failing.

is this not relevant for the newer engines?

[de facto]

I fully agree with JhonT and SN3 Guppy, just Guppy, in 737 we clean up first before selecting MCT,then keep that thrust setting until level off at a safe altitude.

With derate,unless some really feels wrong,leave the remaining thrust alone.
If you need this extra thrust,get rid of the ASSUME using FMC N1 but NO TOGA or fire wall

[390cruise]

Guys

We don't all agree but the discussion is healthy so we can all learn.

Am I a little out of date if I recall that in the V1 continue case we will clear the end (screen height) by 35' or more if the all factors are correct?

I strongly believe that most Airline jets depart at up to 5% above the takeoff mass shown on the load sheet.

The culture of 'save the good engine' dates from the piston era.

Engine failure are rare, will really notice if 'something feels wrong' to increase power? when so much is already wrong.

Also at high masses Vmca is not a problem, while at low masses thrust is not such a problem and anyway speed tends to run away!!!

Yes I agree with John respect Vmc, thrust up with care and practise the whole thing in the sim.

390

[lomapaseo]

one of the most compelling reasons not to increase thrust that I learned from early jet aircraft literature, is that the more thrust you demand from an engine, the higher the chances of it failing.

is this not relevant for the newer engines?


Not true for normaly functioning engines, but is true for a malfunctiong engine.

As always, fly the aircraft and don't just do stuff without thinking first.

Hopefully the finer points of this are covered in your training.

Dithering one throttle at a time is fine, but firing a bottle is permanent

[Escape Path]

Am I a little out of date if I recall that in the V1 continue case we will clear the end (screen height) by 35' or more if the all factors are correct?

Hi 390,

I think it's 50ft screen height when the runway is dry and 35ft screen height when the runway is wet.

Oh, and BTW, as MCT is a lower setting than T/O thrust, and taking into consideration that engines are usually certified to run at TOP for 5 or 10 mins, would it be "wise" leaving the good engine at the TOP setting for, say 4 or 9 minutes (depending on the limitation) when an engine fails? That way you get some little extra thrust much needed to get away from planet Earth.

[Mad (Flt) Scientist]

Am I a little out of date if I recall that in the V1 continue case we will clear the end (screen height) by 35' or more if the all factors are correct?

Whatever the specific height is achieved (a function of the rules and conditions assumed) it needs to be borne in mind that the calculation is valid only for the conditions assumed. Specifically for engine failure, it is assumed that the engine (or at least the fan, for sure) is windmilling; if it locks for any reason, which may be the same reason as causes the failure, the performance sums are out of the window and all bets are off.

I strongly believe that most Airline jets depart at up to 5% above the takeoff mass shown on the load sheet.
I'll pretend I didn't hear that .. la-la-la.

Also at high masses Vmca is not a problem, while at low masses thrust is not such a problem and anyway speed tends to run away!!!
Correct for the first part, for the second, not if you have flexed to the max - you just made a low weight takeoff climb or distance limited as well.


An additional thought, which follows from my first point, which is that the need for increasing thrust above the planned level to actually climb may arise due to a failure case not considered in the performance calcs - that same unanticipoated failure case is likely also outside the scope of the failures assumed for handling, and the official VMC may now be purely notional.

Indeed, in a worst case scenario with a locked fan, say, not only is the drag well above the assumed levels resulting in badly degraded performance, but the drag is also increasing the control requirements even WITHOUT increasing the thrust, and it may in fact be impossible to square that circle. Some failures will not be survivable... no matter what you do with the thrust levers.

[renard]

Well on the plane I fly, E170/E190, in an engine failure on T/O I don't have any say in the matter of increasing thrust on the live engine.

The Automatic Takeoff Thrust Control System will command RSV thrust if it detects an engine failure on take off, go-around or windshear.

If I use TO-3, no flex, max thrust is 11800 lbf. An engine failure will boost thrust to 13000 lbf, without me taking any action.

Do other aircraft have a similar system?

[lomapaseo]

Indeed, in a worst case scenario with a locked fan, say, not only is the drag well above the assumed levels resulting in badly degraded performance, but the drag is also increasing the control requirements even WITHOUT increasing the thrust, and it may in fact be impossible to square that circle. Some failures will not be survivable... no matter what you do with the thrust levers.

I would discount the locked fan scenario as not realistic or valid.

The drag characteristics are set by the inlet frontal area and not the engine fan where the spaces between blades are great enough to let the air out the by-pass. Engine spillage effects are only temporary in nature and typically associated with engine surge.

All this not withstanding flight simulator training.

[galaxy flyer]

Renard

I believe the APR thrust increase will be an increment above the derate, not to the full APR without the derate selected. If that is not the case, performance must be based on Vmcg and Vmca, if applicable, for the full thrust. In any case, those speeds must be calculated on the APR thrust.

In fact, the APR probably only add an increment above any reduced power set, if the throttles are left alone.

GF

[PEI_3721]

Renard, IIRC the HS125 used an APR system (automatic performance reserve), and this was not a matter of simply increasing thrust. Memory is failing, but AFAIR the thrust increase after an after an engine failure was to achieve the value necessary to meet the minimum performance; thus it is a necessary increase.
There is an AC / Regulation on this somewhere (I’m looking), but I note that aircraft which use such systems have low thrust asymmetry with engine failure, i.e. centre-line engines.

[Mad (Flt) Scientist]

I would discount the locked fan scenario as not realistic or valid.

The drag characteristics are set by the inlet frontal area and not the engine fan where the spaces between blades are great enough to let the air out the by-pass. Engine spillage effects are only temporary in nature and typically associated with engine surge.

All this not withstanding flight simulator training.

I agree, locjked fans are unlikely. But the scenario being postulated - the need for a crew to increase thrust above that planned to achieve the regulated takeoff performance - is itself an inherently unlikely scenario. 9.9...% of the time there will be no need to even exercise the reasoning being discussed in this thread - leave the thrust where it is and everything just happens by the book.

My point was to highlight that the same kind of scenario where you may have a need for excess thrust over the planned level may also have consequences for other aspects of the aircraft, such as handling, and all would need to be considered before pushing the levers up.

I know of one engine failure event where, due to the nature of the failure, the aircraft was barely able to sustain an altitude which was some 10,000ft below the advertised single engine capability. It all came down to much greater drag from the failed engine than for the assumed windmilling case. If that had occurred on takeoff, the considerations I mentioned would have applied - and I suspect it might not have been survivable, even with firewalling the engines being an option.

[Mad (Flt) Scientist]

Renard

I believe the APR thrust increase will be an increment above the derate, not to the full APR without the derate selected. If that is not the case, performance must be based on Vmcg and Vmca, if applicable, for the full thrust. In any case, those speeds must be calculated on the APR thrust.

In fact, the APR probably only add an increment above any reduced power set, if the throttles are left alone.

GF

From memory, APR (or ATTCS to use the FAA term) works EITHER way depending on the type. Sometimes its a delta to the current set thrust, and that's typical for a mechanically controlled engine; I believe other cases, which are some (but I can't say all) FADECs will actually go to a rated single engine thrust, rather than a delta to the current all-engines set. (assuming flexing is being done)

If there is a derate - as opposed to a flex - then there will likely be an APR set corresponding to each derate, for the reasons you mentioned.

[Mad (Flt) Scientist]

@PEI : § 25.904 Automatic takeoff thrust control system (ATTCS) and Appendix I are what you're referring to I think. There is an AC also, from memory.

Ac25-13 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2025-13/$FILE/AC25-13.pdf), which is really about derate and reduced power takeoffs, does contain some passing references to ATTCS. I cant find one specifically for ATTCS.

[galaxy flyer]

Thanks for that, MfS. FYI, when I was employed by Eastern, a BOS crew on a DC-9-50 (powered by JT8D-9 or -11 engines) had an uncontained failure departing KTPA. I believe that had a locked engine or, at least a failure that induced considerable drag in the windmilling engine, and various bits of cowling hanging out in the breeze that reduced performance to the point the crew couldn't climb above about 500 AGL and considered ditching in the Bay. In any case, I flew with the F/O and he was pretty convinced that ditching was a possibility despite "firewalling" the throttle on the operating engine.

GF

[lomapaseo]

Thanks for that, MfS. FYI, when I was employed by Eastern, a BOS crew on a DC-9-50 (powered by JT8D-9 or -11 engines) had an uncontained failure departing KTPA. I believe that had a locked engine or, at least a failure that induced considerable drag in the windmilling engine, and various bits of cowling hanging out in the breeze that reduced performance to the point the crew couldn't climb above about 500 AGL and considered ditching in the Bay. In any case, I flew with the F/O and he was pretty convinced that ditching was a possibility despite "firewalling" the throttle on the operating engine.

GF


It was the drag from the half blown off nacelle (burner case rupture) and as you say quite dicey to make the ATB. A wake up lesson about a half dislodged nacelle on a failed engine can = more than an engine out effect.

[aterpster]

Escape Path:

I think it's 50ft screen height when the runway is dry and 35ft screen height when the runway is wet.

35 and 15 feet, respectively.

[Escape Path]

Thanks a lot for your correction aterpster. :ok:

Do other aircraft have a similar system?

Yup, Dash 8's autofeather (when armed and fully operational) should feather the failing engine prop and add 10% nominal torque to the live engine. It's called Power Uptrim in the DHC-8. When in the sim (suprisingly) the autofeather doesn't do it's job, laughter ensues.

May I re-ask my question? :E

Oh, and BTW, as MCT is a lower setting than T/O thrust, and taking into consideration that engines are usually certified to run at TOP for 5 or 10 mins, would it be "wise" leaving the good engine at the TOP setting for, say 4 or 9 minutes (depending on the limitation) when an engine fails? That way you get some little extra thrust much needed to get away from planet Earth

Best regards,

Escape Path

[Mad (Flt) Scientist]

May I re-ask my question? :E

Oh, and BTW, as MCT is a lower setting than T/O thrust, and taking into consideration that engines are usually certified to run at TOP for 5 or 10 mins, would it be "wise" leaving the good engine at the TOP setting for, say 4 or 9 minutes (depending on the limitation) when an engine fails? That way you get some little extra thrust much needed to get away from planet Earth


I would suggest that you leave the engine running at TOP for as long as required; ordinarily that will be a shorter period of time than the "approved time" for that rating to be used.

But if for whatever reason you are still "in trouble" when the clock ticks over that magic limit, there's no reason to pull back the power and possibly make a bad situation worse. If you need the thrust, you need the thrust. There's only one place it can come from.

And in making that judgement as to when it is appropriate to breach the engine operating limitations, it should be borne in mind that the engine is not designed to fail at 5 mins and 1 second; it's designed to run dependably for 5 minutes. It may in fact do a lot better than the 5 minutes, it just isn't approved to do so, and the likelihood of it keeping going will start decreasing the more you abuse it. But if it's a choice between abusing the engine and hitting terrain ... and by the same token, once you don't need the engine to complete the takeoff climb, it does make sense to baby it a bit and not push it any harder than you need. After all, the other engine just failed after a lot less than 5 minutes at rated power .. why take any chances with what may be your last engine...

[Escape Path]

Thanks for the input MFS.

Much appreciated.

[390cruise]

A couple of points,

While I am a bit out of date I believe the 50' and 35' as stated by 'Escape path' rather than the 35' and 15' put forward by aterpster. Perhaps these numbers are used in another part of the world?

The five or ten minute limits for max thrust relate to factors regarding the long term life of the engine.

390

[john_tullamarine]

While I am a bit out of date I believe the 50' and 35' as stated by 'Escape path' rather than the 35' and 15' put forward by aterpster. Perhaps these numbers are used in another part of the world?

50 ft screen dates back to the very early days of the US regulators. According to a chap of great antiquity who was a young fellow back in the early post-earliest days of the regulator (probably no longer with us - he related the tale on a course I attended about 20 years ago), the story was that it derived from a military demonstration into a parade ground surrounded by (about) 50ft high trees ..

That figure was then adopted in the civil world. Subsequently, it remained the requirement for lighties both for takeoff and landing. However, as I recall at the time that the ICAO PAMC came into vogue (early F27 days) the takeoff screen for heavies reduced to 35ft, where it remains today.

Very much later, with the introduction of a degree of formalised discipline with respect to contaminated runway operations, there arose a permission to use a reduced screen of 15ft for such calculations.

As an aside, aterpster is quite expert in these operational matters ...

The five or ten minute limits for max thrust relate to factors regarding the long term life of the engine.

That may well be true. However, the certificated (read legal) limit at takeoff thrust is either 5 or 10 minutes according to the Type.

[fdr]

Hi JT:

35'/15' min when wet, FAR 25.111(c) (2), 25.113 (a)(1), and 25.113 (a)(2) (all engine...) alternatively CAO 20.7.1B, Para 7 (had a nice discusion about wet screen in the past...). FAR 25.113(b)(2) covers wet for the Gringo's... 15'.

50' does crop up in other matters... (various ICAO docs re procedures...) but not screen height at end of TODA.


cheers, and happy METO settin'

FDR

[390cruise]

OK

After a quick 'Google' I agree 35' and 15'

(sorry guys)

I still stick to my other points though!!!

390