Use of ATM

[kuobin]

Hello gentelmans:
One company's runway analysis manual has a limitation like this:

Using ATM is prohibited under the following conditions:
1.Brake deactivated or anti-skid INOP.
2.Takeoff runway is contiminated
3.De-ice fluid applied.
4.LVO takeoff.

Can anyone provide the reason behind.and what about Derate.Is derate OK?:ooh:

[Intruder]

What is ATM? What airplane?

If you mean Assumed Temperature Method Reduced Thrust, you have to go by your airline's SOP and Performance manuals. Certifications differ widely among airlines, and the performance manuals are based on those certifications.

[safetypee]

Reduced Thrust using ATM results in a longer take off run. The conditions under which the restrictions apply have increased risk whilst on the ground. Thus, the use of full thrust gets the aircraft off the ground quicker, reducing the risk, but not necessarily to the normal, non-restricted value.
Brake deactivated or anti-skid INOP – in case of an Rejected Take Off.
Takeoff runway is contaminated – RTO considerations and slush drag during takeoff, or low friction / crosswind control.
De-ice fluid applied – potential drag increment, reduced lift and/or trim (rotation) issues – aircraft type dependant.
LVO takeoff – questionable, but it is better not to be on the runway if you can’t see objects.

Reduced thrust (ATM) is not the same as derate – see previous thread (www.pprune.org/forums/showthread.php?t=190430&highlight=derate
) post #5.

Derate is a fixed thrust value, but less than the engine is certificated to produce. It is the agreed maximum thrust for the engine installation/use. The AFM aircraft handling limitations, Vmcg etc are based on this value. Therefore any higher value of thrust cannot be used (there may be specific exceptions).

With reduced thrust, the thrust level may be restored to the full value (but not greater than the derate value if applicable to your type).
Takeoff performance and aircraft handling considerations do not require any thrust increase in the event of an engine failure.
If your aircraft uses derated engines and reduced thrust is an approved operation then I assume that the restrictions also apply.

[barit1]

25 years ago I wrote a brief for my management explaining the distinction between "reduced" and "derated" thrust - it's essentially that derated ops are based on actual flight test data, whereis ATM reduced thrust (FAA Order 8000.39 applied in those days) involved some conservative extrapolation, and thus additional conditions applied. (For my sterling efforts, I received a pink slip; they shot the messenger) :ugh:

For maximum operational flexibilty, an operator should have both protocols available.

The current document is FAA Advisory Circular (AC) 25-13; I haven't explored it in great detail, but I doubt it invalidates the prior order.

[kuobin]

The type of airplane is B744,
So now I can understand in order to avoid unnecessary exposure to contaminated runway ,The use of max rated thrust to get off the ground ASAP is reasonable.
For anti-skid inop or brake deactivated .It is because in these conditions, after takeoff you have to wait for two minutes for wheels to spin down before retract landing gear. Thus climb capability is greatly reduced , this is why you have to use max thrust for takeoff.
Still don't know why we cannot use ATM after application of anti-ice fluid, because we don't have to make any adjustment of airplane performance after anti-iced.:ooh:

[FE Hoppy]

Think of it this way.
Reduced thrust(ATM) is an attempt to use the minmum thrust required to take off in the distance available. You could have a thrust level that will put you at 35/15 ft at the end of TODA in the OEI go case or stop you at the end of ASDA in the OEI stop case. Therefore anything that may compromise the performance should restrict the use of ATM. Anti-ice fluid will to some degree compromise your aerofoil and therefore its safer to use more thrust that required.
It's a somewhat simplified explanation but I hope it helps.

[Capt Chambo]

Just a couple of points, more specific to the B737. The use of ATM after anticing/de-icing or during LVOs is company specific.
The use of the ATM would also be prohibited when an engine power guage is u/s (EPR or N1).
Kuobin the wheel rotation is stopped before/during gear retraction by the brake system and whether the anti-skid is operational or not should have no bearing on the matter. The reason that the use of the ATM is prohibited without anti-skid is the greater stopping distance required. The use of full power should mean you arrive at your V1 speed sooner, which translates into less distance travelled down the runway, which in turn gives you more runway to stop on if you abort the take-off.
Inop. anti-skid has possibly the largest effect on the B737's performance, depending on the model you are talking about, reducing your take-off weight by about 8000Kgs, and it also has the single greatest effect on landing performance too.
Apologies for aircraft type creep!

[kuobin]

Dear Capt Chambo:
Today I check B738 Mel .find there is no dispatch relief for wheel brake inoperative,
But for B744 you can be dispatched with max 2 of 16 wheel brake inoperative either by cap hydraulic line or remove the brake ,same procedure applied to anti-skid system, when anti-skid function for certain wheel is inoperative ,you can deactivate that brake and dispatch the airplane .then same thing happen ,there will be no gear-up braking function for the wheel so you have to wait for two minute after takeoff before retract gear.
Now I am clear on not using ATM for anti-skid inoperative ,but what about fixed derate,:rolleyes: say B738 has 22k or 24k derate .are they OK for anti-skid inoperative .Thanks.

[barit1]

It may be that the derate section of the AFM contains cert. data for anti-skid inoperative; this may be the case of the airplane originally cert. with early model engines, and later with uprated engines. In that case, flying to the earlier thrust rating is treated as a derate of the later engine model.

(Example: A300B2/B4 and DC-10-30 originally cert. with CF6-50A engines, later uprated to -50C, -50C2 etc. The -50A AFM chapter is still available as a derate to later engines.) :8