Thrust reduction altitude
 

Hello guys,

Can we set climb thrust at 800 ft when the take off performance chart is based on a Flaps retraction Altitude of 1000 ft AGL?
Flaps retraction altitude is the 3rd segment of take off path.which means in case of engine failure we are supposed to climb with a take off thrust until the acceleration segment.

Should an engine failure occur at 900 ft AGL, can we say that we are still in the 2nd segment with no take off thrust?

2nd segment of take off assumes to have some requirements ( flaps at take off etcc.. ) among which take off thrust is mandatory and there are only 2 take off thrust toga or flex.

If the Flaps retraction altitude is modified on the take off performance chart is it going to affect the flex temperature? And weight penalty?

Finally can we set climb thrust at an altitude lower than the flaps Retraction altitude showed on the take off performance chart?

Thanks for your inputs

Good Question. In my aircraft, the runway analysis is based on a single engine performance, not two engines performance. It just would require that you are in APR thrust until final segment climb then to MCT.

If you reduce to climb thrust at 800 feet, to meet runway analysis you probably need to go to APR if engine failure after 800 feet.

Sorry what do you mean by APR?

APR is just another way of saying Max Thrust. I guess my post doesn't mean anything compared to the aircraft you are flying. Sorry for that.

Not really, its more of a Thrust Bump than Max Thrust.

Citation2, what are you trying to achieve? Why cant you follow the prescribed profile?

Mutt

isn,t apr only relevant in single engine operation above a certain flat rated temperature ? i thought that below that pushing the apr notch still commands the normal take off thrust - in other words, no changes in output.

best regards

I think they're might be more than one definition of APR, so you're going to need to get specific.

APR on a SF340B give you 7% more torque if you have an auto-coarsen, IIRC. 7% more than what you had, be it reduced or 100%.


Now back to your scheduled thread drift. . .

I understand you would put Max thrust when the engine fails but for a second you were in the second segment without take off thrust.

Legally speaking and not talking about aircraft capability.Is it correct to set climb thrust before Flaps retraction Altitude which corresponds to the 3rd segment.

If the runway analysis is based on a Flap retraction Altitude of 1000 AGL it means that it assumed take off thrust until 1000.

Therefore all weight limitations and assumed temperature given for the condition of the day, which satisifies the 2nd segment requirement ( 2.4% gradient gross , obstacle clearance etc..) assumes Take off thrust until you reach 1000

Now if you reduce thrust before 1000 maybe the assumed or flex temperature given on the chart or the take off weight , are not valid anymore since you are in climb thrust in the second segment . So not respecting one condition for which all the datas are calculated for.

My point of view is that if the charts are based on 1000 AGL weight penalties or assumed temperature are going to be so and so. if based on 800 agl assumed temperature going to be lower because you would have to clear the same obstacles with a shorter time in take off thrust , so you need more power and then a lower assumed temp.

Am I correct?
So again , is it correct to set clmb thrust at 800 when the flaps retraction altitude on take off performance chart is 1000 ?

This is one of those rubbery things, I fear.

Takeoff per AFM is based on OEI.

Routine takeoff is based on AEO.

During a routine takeoff,

(a) especially on twins

(b) providing that the AEO procedure adopted is conservative with respect to the OEI

(c) providing that tracking is the same as for the OEI procedure

(d) presuming that thrust remains at TO until the final climb speed and configuration is achieved

the aircraft gross flight path will be above the OEI calculated net flight path by a considerable margin. The end result is that a modest difference between AEO and OEI acceleration is not going to compromise the OEI situation.

Your ops eng cell should have appropriate words in the RTOW chart procedure to cover the situation for a specific runway departure.

I am not aware of any regulatory words which address this situation.


but for a second you were in the second segment without take off thrust

Probably not a major consideration as you should be well above the NFP and at a higher speed. In such circumstances, one can always select back to TO thrust should that be deemed necessary by the Commander.

which satisifies the 2nd segment requirement ( 2.4% gradient gross , obstacle clearance etc..) assumes Take off thrust until you reach 1000

.. and includes OEI, not AEO.

My thoughts are

(a) if AEO tracking differs from OEI escape, then all bets are off unless the ops eng cell has done the sums for a post-V1 failure

(b) if you are concerned, then use Commander's prerogative to delay thrust reduction until the higher level.

(c) go knock loudly on the the ops eng cell's door and ask the question of the folk who should have the answer.

If you have a OEI acceleration altitude of 1400 feet, do you delay thrust reduction AEO to 1400 feet?
In my outfit we don't, if both engines have been giving power up to 1000feet we select climb thrust even though our OEI acceleration altitude is 1400 feet. I think that answers the question in line with what JT was saying, ie you've rocketed up there on two engines so you have well and truly outperformed the V1 go scenario.

AFAIK, no. I have not seen a situation where thrust is reduced until clean with OEI.

In the 747, when AEO acceleration height is 1000', the thrust reduction is at flap retraction to 5 (T/O flap is 10 or 20). If an engine fails prior to 1000', T/O thrust is held until clean.

I am talking about a normal take off with two engines. Your perfromance from runway analysis are bases on a flap retraction altitude of 1000 AGL of course taking into consideration one engine out.

Now considering a normal take off with two engines , for some reasons you decide to reduce thrust at 800 AGL ( noise abatement, fuel saving policy etc..)

Should an engine fail at that moment? Are you protected? Because the performance calculated on the runway analysis are based on a flap retraction altitude of 1000 so they assume take off thrust until at least flaps retraction altitude.
Your max weight , assumed temperature , all lmitations calculated are based on a take off thrust until 1000.
So if you take off with 2 engines and decide to reduce thrust at 800 are you protected or is it legal?

Well yes you are protected since for the first 800 feet you have climbed on 2 engines well in excess of the minimum gragient required for 1 engine flameout at v1.

Protected from what?!? If you decide for some reason to do something NOT according to accepted standards, what "protection" do you expect?

Reducing thrust for climb does NOT save fuel, because it reduces climb rate and acceleration to best climb speed.

Standard noise abatement profiles do NOT require thrust reduction below 1,000'.

Why would you put extra stress on your remaining engine by using APR, solely because you decided to do something nonstandard?

I think that Capt Glenn is the only one that understood my point.
I agree with you CApt GLenn, as so far you climbed with 2 engines, so of course your gradient is much higher than the one of single engine. But do you know of how much higher? What would be the convergency from the 2 engines gradient to the single engine gradient?

At the engine failure "time" you were in a situation in which you are in CLMB Thrust ,and still in the second segment
Of course you would put max thrust but during a second you were in clmb thrust in the second segment of take off path

From a legal point of view is it okay? Not talking about aircraft capability.

I would definitively not accelerate below 1000agl ..both engines never below single engine min acc height.
Thrust reduction can be initiated above 800 and prior to 1500 aal for noise reasons.
For higher oei acc height (innsbruck for example),special procedure are built and noise may not be the airport priority...
If i remember correctly t/o 26 ,few deg to right,then 1500 climb thrust,once the 180 left turn completed above airport ,acceleration.

It's either 'heaps' or ' sh1t loads' I can't remember which.
Don't worry about it from a legal perspective (unless you're a lawyer) just make common sense decisions about what is safe and what is not.

Considering the OP - for OEI 1000ft and AEO 800ft, there are too many variations to be specific.

However, presuming that the AEO thrust cut doesn't involve flying level (and, apart from cloud chasing (or coastal pax scenery viewing - maybe folks don't do that anymore ?), I can't see why one might want to do that - an ATC level restriction at 800ft is not all that likely to occur, I suspect), and an initial AEO climb at, say, 10%, one needs only an average climb of around 0.4% to keep above the gross profile at WAT limits from 800ft through 1000 ft.

Now, while one should do the sums for a specific Type and operation, it is UNLIKELY to present a problem for the aircraft's flight path terrain clearance during that delta. Indeed, the terrain clearance sums are much more conservative than most pilots might presume as the calculations for terrain clearance put the calculated aircraft height on the NFP substantially BELOW 1000ft.

The commander really has a few more important priorities than this sideline "interesting" consideration ..

One more time...

From a legal/practical/defending your decision and ticket if you mess it up point of view, WHY WOULD YOU DO IT IN THE FIRST PLACE?!?

There is NO justification I can think of that would give the Feds ANY REASON to do anything other than crucify you for a "reckless or careless" decision. In a critical phase of flight, intentionally doing something less safe than an accepted standard, thereby putting your passengers or the public at higher risk, is certainly within MY definition of reckless!

It's not just a simple decision. The company decided to set thrust reduction altitude at 800 ft , for a normal take off. And it used to be 1500 before.