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B737 Series use of reverse thrust during landing roll

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B737 Series use of reverse thrust during landing roll

Old 15th Apr 2018, 03:58
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B737 Series use of reverse thrust during landing roll

Re use of reverse thrust in the Boeing 737 series.

Edited for brevity from the FCTM:
"Maintain reverse thrust as required, up to maximum, until the airspeed approaches 60 knots...

...The thrust levers should be positioned to reverse idle by taxi speed then full down after the engines have decelerated to idle. Reverse thrust is reduced to idle between 60 knots and taxi speed to prevent engine exhaust re-ingestion and reduce the risk of FOD.... The PM should call out 60 knots to assist the PF in scheduling reverse thrust."

Question: If landing into a (say) 30 knot HW component, 60 knots IAS means a 30 knot ground speed. The slower the aircraft is on the ground while using high reverse thrust, increases the risk of FOD and engine surge.

Would it therefore be true to say that reverse thrust should be positioned to idle at 60 knots ground speed if landing into wind, rather than 60 knots airspeed?
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Old 15th Apr 2018, 04:14
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A long time since I flew a B737 Centaurus, but the text is exactly the same in the B777 FCTM.

The pertinent phrase is ďas requiredĒ. With a 60 kt headwind component, the speed trend arrow will be Big because the airplane would have a GS at Touchdown of maybe 80 Kts.

I taught my students to always go to the second detent and apply reverse thrust. With the aircraft under control and decelerating, then eyeball the desired exit point and estimate the deceleration. Then reduce the reverse thrust as desired so as to be able to stow the reversers after 60 knots and at idle reverse.

The only inertia computers are biological, and the pilots are the only ones able to do this successfully, repetitively. Airbus has Brake To Vacate (BTV) on their A380 and only two reversers. The BTV computer often applies Max Braking unnecessarily. AI is still modifying the software.

It is the old stroy of judgement, which comes with experience.
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Old 15th Apr 2018, 04:42
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Would it be too simplistic to say the wind helps blow the FOD away?

Probably... or maybe it's simpler to run with IAS and 30kts across the ground (using your 60kt ias, 30kt h/w) isn't that big of a risk?
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Old 15th Apr 2018, 08:37
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This is an interesting question.When I used to make the odd landing at an airfield around 8000 amsl even with no wind, there was a very big split between IAS and Groundspeed.At the stipulated "60 knots" if you used IAS as your guide the groundspeed could be much higher.The various (Boeing) FCTMs do not differentiate between IAS and GS so to be conservative I used the higher indication and delayed reverse thrust reduction until the GS indicated 60 ignoring the PMs call of "60 knots".Never had any issues.....
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Old 15th Apr 2018, 10:21
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Originally Posted by Centaurus View Post
Re use of reverse thrust in the Boeing 737 series.

Edited for brevity from the FCTM:
"Maintain reverse thrust as required, up to maximum, until the airspeed approaches 60 knots...


Would it therefore be true to say that reverse thrust should be positioned to idle at 60 knots ground speed if landing into wind, rather than 60 knots airspeed?
I strongly suspect that if Boeing decided to use the term airspeed then they did consider several factors and still decided to use that specific term, hence I wouldn't get myself into rewriting a personal copy of the FCTM.
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Old 15th Apr 2018, 13:22
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It's the air, not the ground, that blows the forward-tending efflux backward and away from the intake lip.


Neat video shot from the cabin, of an engine during reverse, with a wet runway. You can see the point where the efflux splashes the water moving forward as the airspeed reduces.

Last edited by Vessbot; 15th Apr 2018 at 13:32.
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Old 15th Apr 2018, 14:11
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Pilots love numbers & limits. 60kts, or whatever speed is a limit. As 3 Wire said, use TR's until they are no longer required. If the turnoff is a long way off why keep them open? They are very ineffective at slow speeds anyway. It is not necessary to wait until 60kts to stow them.
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Old 15th Apr 2018, 15:47
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I've normally found that a 30kt headwind normally negates the requirement to use full reverse for brake cooling requirements...
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Old 16th Apr 2018, 07:18
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I've normally found that a 30kt headwind normally negates the requirement to use full reverse for brake cooling requirements...
Depends on runway length and surface conditions. Short wet runway for example.
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Old 16th Apr 2018, 15:10
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Cool

Use the reverse thrust as long as requires, simple.

But looking at part of your question, you ask:
Originally Posted by Centaurus View Post
Would it therefore be true to say that reverse thrust should be positioned to idle at 60 knots ground speed if landing into wind, rather than 60 knots airspeed?
Very old question and the answer should be YES, but alas most airlines only refers to airspeed in FCOM on many types.

It has been a long standing argument in many operations, as the philosophy seems simple:
* use airspeed when wanting to get airborne as we need lift and this is generated by air over wings which is measured by IAS on instruments;
* use groundspeed when wanting to stop on the ground as we need to come to a safe taxi speed which is based on GS on instruments;

If only management would read this thread...
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Old 16th Apr 2018, 22:23
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Skyjob,
Thats a really good way to describe the issue, I like it.Problem is the FCOMs only make reference to "airspeed".Most SOP/STANDARD CALLOUTS are only ever referenced to IAS ...and this is what you hear from your PM.I choose, when appropriate, to ignore the call and begin reducing reverse towards idle at 60 knots groundspeed.The type I fly has an issue with hot brakes.....
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Old 16th Apr 2018, 23:28
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The 60 knot callout is airspeed, because airspeed is what matters to the reverser and engine. The primary reason you don't want more than reverse idle at 60 knots is to prevent re-ingestion. Re-ingestion can cause a surge or FOD damage - again it's airspeed that is the primary determinate of re-ingestion (there are some potential FOD scenarios where ground speed also comes into play, but those a relatively uncommon).
Using ground speed would effectively mean different procedures for head wind and tail wind landings unless you want to use both (e.g. 'when airspeed or groundspeed is less than 60 knots').
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Old 18th Apr 2018, 14:10
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I normally completely ignore the Boeing manuals. I know a lot more about flying Boeings than Boeing do.
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Old 18th Apr 2018, 19:58
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Originally Posted by Judd View Post
Depends on runway length and surface conditions. Short wet runway for example.
Then that's not just brake cooling requirements!
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Old 28th Jan 2020, 18:55
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Thrust reverse use

Is it mandatory to set reverse to idle at landing even when we donít require its use??
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Old 30th Jan 2020, 00:12
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As taxi speed is referenced to ground speed I would assume the preceeding 60kts would also be a ground speed regardless of wind. Otherwise it starts getting complicated if you consider landing with a tailwind and potentially stowing the reversers at a higher ground speed..
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Old 30th Jan 2020, 03:03
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Is it mandatory to set reverse to idle at landing even when we donít require its use??
I donít believe it is mandatory, but I believe that it is wise.
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Old 30th Jan 2020, 06:08
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Originally Posted by Starboard777 View Post
Is it mandatory to set reverse to idle at landing even when we donít require its use??
Why wouldn't you want to use at least idle reverse?
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Old 30th Jan 2020, 20:25
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Originally Posted by Oakape View Post
I donít believe it is mandatory, but I believe that it is wise.
I was always in the understanding that it was mandatory, to get rid of the forward thrust vector, even at idle.
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Old 31st Jan 2020, 06:55
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Over the years of Boeing 737 simulator training with crews from various airlines we see quite a few variations in use of reverse for landing. .

The FCTM states in part: "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"

In the simulator it is common to see the PF either cancelling reverse thrust by lowering the reverse levers all the way down at the call of 60 knots (instead of stopping at the reverse idle detent) or, in attempting to locate the reverse idle detent by feel, the PF lowers the reverse levers too far and it becomes forward thrust (not desirable for obvious reasons).

Some pilots deliberately choose to cancel full reverse at the call of 60 knots by smartly placing the reverse thrust levers all the way down. When that happens the N1 takes time to wind down from full reverse. It is during the wind down period the N1 will be rapidly passing through around 60% N1 as the reverse sleeves fully close, leaving the engine momentarily passing a figure of around 55% to 60% N1 in forward thrust. (again undesirable for obvious reasons). Instead of slowing up, the aircraft then momentarily accelerates along the runway due to relatively high N1 in forward thrust on the way down to idle N1

For various reasons, occasionally the PNF fails to call "60 Knots." Usually something else has taken his attention or because he is staring outside the windscreen. In the absence of the "60 knot" call from the other pilot, the PF should start reducing to idle reverse based on his own ASI reading and not relying on a call-out from the PNF to remind him what to do. Surely this is nothing more than a matter of good airmanship and knowledge of the Boeing FCTM published procedures?

Finally, a word about use of reverse thrust for landing on slippery runway operations with a significant crosswind component. Readers can study the appropriate Boeing FCTM advice at their leisure. But read it carefully especially the advice on reverse idle selection and use of brakes. Some operators prefer to have the PNF operating the reverse levers on all landings - dry or slippery. This relies heavily on accurate directions from the PF to the PNF at a dynamic time. If the aircraft starts sliding sideways on a slippery runway then it is vital the PF take over operation of the reverse levers. Some juggling of brakes in conjunction with reverse thrust will be needed and there is no time to call out instructions to the PNF.
Read the diagram published in the FCTM to see what I mean.

Last edited by Centaurus; 31st Jan 2020 at 07:31.
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