B737- Reverse Thrust Operation.

[Tee Emm]

With regard to using reverse thrust after landing the FCTM states (page 6.29)

Maintain reverse thrust as required, up to maximum, until the airspeed approaches 60 knots. At this point start reducing the reverse thrust so that the reverse thrust levers are moving down at a rate commensurate with the deceleration rate of the airplane. The thrust levers should be positioned to reverse idle by taxi speed, then to full down after the engines have decelerated to idle...

There is an apparent contradiction where an airspeed approaching 60 knots is the trigger to take action to reduce reverse yet the thrust levers must be positioned to reverse idle by taxi (ground )speed.

Given a 40 knot HW component on landing, it is obvious that at 60 knots airspeed the ground speed will be 20 knots - which is normal taxi speed and by which, according to the above advice, the reverse should be at idle. The reason 60 knots is chosen is presumably because of the danger of foreign object damage and engine surge at high levels of reverse at slow speeds.

This all suggests the speed at which reverse thrust should be reducing is 60 knots ground speed - not necessarily 60 knots airspeed. This becomes more important given stronger headwind components?

Page 2.5 of the B737 FTCM happens to discuss taxi speed and braking and among other points states: Normal taxi speed is approximately 20 knots adjusted for conditions.

In this case it is clear why "taxi" speed is used - meaning naturally, ground speed. This suggests again, that if the reason for given by Boeing at page 6.29 FCTM, for 60 knots as the target speed for reverse reduction (due to danger of engine instability at lower speeds), then certainly a 20 knot ground speed with high reverse exposes the engine to potential damage.

And by my calculation a 60 knots IAS applied to 40 knots HW component means 20 knot ground speed - and that's a bit too low for engine comfort, n'est ce pas?

Moral of the story? If landing into a strong headwind component it may be wise (in order to minimise the potential for engine instability) to start reducing the reverse thrust at 60 knots ground speed - not 60 knots airspeed. Appreciate opinions.

[BOAC]

I can remember this argument rattling around for years! No-one ever resolved it in my experience. Probably all a bit academic really, since in a 40kt h/w I would probably be out of reverse before that.:ok: It is interesting to watch the reverse spray pattern in different winds on wet runways.

[PantLoad]

This is a reply not only to this thread...but to many others, here at PPrune , as well. Back, many years ago, when I started my airline career, my company SOP manual had written at the bottom of each and every page the following words:

THERE IS NO SUBSTITUTE FOR GOOD JUDGEMENT


Nowadays...seems that everyone has become so pedantic...so ^$%^, that we've lost sight of the forest for the trees.

I remember...all new-hires had a one-on-one meeting with the company president (and founder of the airline) and also a one-on-one meeting with the Director of Flight Ops. The meeting with the president was to 'communicate' the company's mission.

One of the things the president told us..."If I ever hear that you were, at any time, rude or discourteous to a customer, your employment here will be terminated immediately." Man, have things changed over the past 30 years or so!!!

And, with the Director of Ops chin wag, "We pay you to use good judgement in all you do...both in the aircraft, and on the job in other capacities. And, that's what we expect!"

So, in response to this particular discussion regarding the use of thrust reverse, headwinds, landing on a Tuesdays..or whatever...Use common sense and good judgement. You can never go wrong.

PantLoad

[barit1]

Inasmuch as reverser aero behavior can reasonably be correlated with IAS, I'd think Boeing intended the reverser T/L reduction to be keyed on IAS.

The fact that a 40kt headwind might show a 60kt IAS at taxi shouldn't bother reverser operation, should it? I'd be more concerned about tailwind ops.

But if you're looking for an official guideline, ask your Boeing rep! :cool:

[Rainboe]

TM- when you write a set of guidelines, there is always someone who will read them for any possible perceived 'holes'. I believe you should read the manual for 'how would a reasonable person interpret this?'. I think you are being pedantic in the extreme trying to find a hole here. The aim of the game is to get down to idle reverse power translating to forward idle by 20kts. If you have a 60 kt headwind, why would you require to hold reverse power? In fact you would still be OK with reverse power on almost stationary in a 60kt hw component.....but why? In an emergency situation throw the rulebook away, but unless we want a rulebook too heavy to carry, we must accept the guidance in the spirit given, and this smacks of looking for pernickety holes that really aren't there.

In other words, a total waste of time.

[Tee Emm]

Rainbow. Easy does it old chap..

In fact you would still be OK with reverse power on almost stationary in a 60kt hw component.....

Can I quote you on that when the legal eagles coming looking for the perpetrator of a million dollars damage on the engine of one of their clients?

Readers of this thread have misunderstood the point of the original post. It was an academic question which quite frequently is posed by experienced pilots converting to the 737 at the simulator centre. Students quite understandably study closely all the appropriate 737 manuals on these courses and all sorts of questions arise on the intention of some of the Boeing pronouncements. For example the FCTM recommends the speed brake lever position be called (up or down) as part of the after touch down procedure. If it is obvious by it's position such as UP that it is indeed up - then why state the bleeding obvious and call "Speed brake up?" Someone asked the other day, should this also apply to the position of the speed brake lever following a abort - in other words, if the PNF calls "speed brake UP" after touch down then to be consistent with Boeing "philosophy" should not the PNF call "speed brake UP" after the captain selects it to up as part of the abort process. Either by manual selection or automatic operation when reverse thrust is initiated.

Students ask these questions and the simulator instructor can either pour scorn on them like our learned mate Rainbow likes to do to my post - or the instructor can ponder the answer and reply as best he can.

So please do not rip into posts such as this - when it should be crystal clear to any but the cynical and bitter minds, that those that pose certain questions on Pprune are genuinely interested in "Why is this so" and not because of some perceived idiotic pedantic fantasies.:ok:

[outofsynch]

Its gotta be based on AIRspeed. The only reason for when to cancel reverse, is the point you are likely to ingest your exhaust, which has nothing to do with your groundspeed.

Anyway, in my book, there is no point in cancelling reverse, while still pushing on the brakes! "Brakes off = reverse off..."
Select 'forward idle' only when you need some!

[AirRabbit]

I think you’ll find that coming out of reverse is not necessarily because of the potential of ingesting engine exhaust. Rather, as the airplane slows, the effectiveness of reverse thrust becomes substantially less (like a NiCad battery decay slope), so there is less reason to use it; and the slower forward speed you have, the greater potential of experiencing compressor stalls with higher levels of reverse thrust – which, naturally, doesn’t do the engines much good.

[Redline]

Does any other the above make you more attractive to women?

So what's the point?

[Dr Eckener]

TM - I think Pantload offers the best answer to your question. If you are instructing, then you need to be able to deal with questions which may seem important to the student at that stage, but will become irrelevant with experience. The use of good judgement covers this pretty well.

Redline - excellent point.

[AirRabbit]

If I could figure out what would make me more attractive to women, I'd probably be spending less time on the computer....