reverse thrust
 

Hi all.

What is your opinion about using normal reverse thrust on a dry and long runway? (737)
Some told me that is is really stressfull for the engines and it should be avoided whenever possible.:=

Thanks for your comments.

Michael1282

There is a continuing battle between the brakes engineers and the engine engineers about what to do!
But common practice is to select reverse idle only and use the brakes to stop. Brakes nowadays are cheaper than engines.

For a lo-co airline with short (25min) turnround times, brake cooling after landing with idle reverse can be a significant operational factor.

So whilst brakes may be cheaper than engines (though I suspect brakes are replaced somewhat more frequently), if your company requirs short turnrounds then consider that using only idle reverse almost doubles the brake energy.

Check the tables for your aircraft type, and always make sure that your brakes are cool enough to cope with an RTO on the next sector!

Of course, if the runway is really that long then manual braking can be used instead of autobrakes and braking requirements then minimised too.

Ok, these considerations do make sense to me, thanks.
But in fact, it cannot be harmful for the engines to use the reversers; during climbout e.g. we have much higher EGTs for a longer period of time, than during the landing roll out with the reversers deployed.

Don't forget that there is a much greater FOD danger with higher levels of reverse; also some engines are prone to re-ingestion and possible surging - lots of potential for expense there...

True michael, but engine life is reduced whenever the engines are used, so over time the impact of high levels of reverse is to reduce overall life and/or increase engine costs.

However, my personal opinion is that they are installed to improve landing safety - if you elect not to use them you'd better be able to defend your decision in the event of a subsequent runway excursion, whatever the cause.

The key phrase you use here is: "Someone told me" - was that someone quoting from your company Ops manual, and can they show you where? If so, fine; if not: continue to abide by your company-specific approved ops procedures and don't believe everything you hear.

(even on PPRuNe!)

Even though r/t EGT is much lower and for shorter duration than TO & climb, it is still an additional thermal cycle on the engine, therefore a quantifiable cost element. Cheaper than brakes? I'll leave that to someone else to determine.

I concur with FullWings about FOD risk too - not just the massive or obvious FOD, but the more subtle erosive kind that comes from sand or wintertime runway treatment.

But deploying idle reverse early after touchdown is relatively cheap insurance in that it can save a few precious seconds when needed.

If you put the airplane in the weeds at the end of the runway I don't think the investigation will absolve you of any wrong doing if your defence is, "Someone told me".

Any types I have flown with reversers always limits the reverse thrust capability in relation to total engine thrust. Current type (757) is in the order of 1.3 EPR so the thermal cycle is tame in relation to a take-off thermal cycle.

Weigh the thermal cycle against shorter brake only stopping distance, less brake and tire wear. :)

Thank you all very much...

and I think you are quite right when you say:

"some one told me" is not really a good justification

-Thanks

Michael

I believe that modern carbon brakes have been found to actually last longer if subjected to heat. Obviously carbon brakes are more efficient too (hence A380 only has T/R on the inboard engines.

I prefer reversers... much more noise!!!! I use my brakes in my car

extreme P,

Well, I don't know about all types, but in routine operations use of reverse will not decrease stopping distance, certainly on the 73 and by inference other boeings. (though I couldn't swear for your 75)

pb

If by "routine" you mean dry runway and reverse idle, I might agree with you.

Otherwise, read this if you haven't already.

Well, I'm not ploughing through 20 pages of it, but skidding off of a runway doesn't count as normal in my book.

If you are using autobrake, then you get a fixed deceleration. If you use reverse, you get the same deceleration, the brakes aren't applied so hard.

pb

Just by way of interest, the B737 NG fitted with the 27.3K engines, runs about 85% at maximum reverse. I'm not sure of the other engine ratings.

Cheers, FD :ok:

Yeah, but 85% N1 is probably only 60% thrust in FWD mode, and less than that in r/t. :uhoh:

I, heard also many times that CF brake "like heat", but I don't like opining on operational matters as many time the answer is a matter of experience...with jets I have none:ugh:

Makes you wonder why manufacturer's go to the expense of installing thrust reversers when pilots don't use them as recommended in the FCTM.