B737 Series use of reverse thrust during landing roll

[Centaurus]

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?

[Three Wire]

A long time since I flew a B737 Centaurus, but the text is exactly the same in the B777 FCTM.

The pertinent phrase is “as required”. 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.

[Car RAMROD]

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?

[piratepete]

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.....

[sonicbum]

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.:suspect:

[Vessbot]

It's the air, not the ground, that blows the forward-tending efflux backward and away from the intake lip.

https://youtu.be/VrETuZeahbg

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.

[RAT 5]

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.

[Cough]

I've normally found that a 30kt headwind normally negates the requirement to use full reverse for brake cooling requirements...

[Judd]

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.

[Skyjob]

Use the reverse thrust as long as requires, simple.

But looking at part of your question, you ask:
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...

[piratepete]

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.....

[tdracer]

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').

[Derfred]

I normally completely ignore the Boeing manuals. I know a lot more about flying Boeings than Boeing do.

[Cough]

Depends on runway length and surface conditions. Short wet runway for example.

Then that's not just brake cooling requirements!

[Starboard777]

Is it mandatory to set reverse to idle at landing even when we don’t require its use??

[The Banjo]

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..

[Oakape]

Is it mandatory to set reverse to idle at landing even when we don’t require its use??

I don’t believe it is mandatory, but I believe that it is wise.

[FlyingStone]

Is it mandatory to set reverse to idle at landing even when we don’t require its use??

Why wouldn't you want to use at least idle reverse?

[Skyjob]

I don’t 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.

[Centaurus]

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.

[retired guy]

I was always in the understanding that it was mandatory, to get rid of the forward thrust vector, even at idle.

That's it Skyjob
How many accidents have there been because even idle reverse was not selected, which gets rid of the considerable forward thrust from the engines at idle? I can think of so many.
If you don't select reverse idle, you are in fact braking against engine thrust which is going to increase brake wear and heating, even if performance is not an issue.
And even Reverse idle contributes some additional deceleration.
Crank it up to full reverse especially at high speed say >100 its and it really kicks in. Much more effective at high airspeeds hence the need to select right after touchdown. the 737-200 which could reverse almost the entire jet flux being low by pass, using giant buckets, and could stop on reverse alone in about 1800 metres. Landing in Jersey on a wet runway at 1650 metres it was a godsend.
Many of the later High By Pass engines seem to just be big noise machines but even so you are probably reversing 40% of the max thrust - just an estimate. Review any good video of reverse in operation on a wet runway during testing and you can see it is still a big player.
The 737-200 had 15000 lbs of thrust, most of that was directed forwards but because of the angle of about 45 degrees deflection we used to reckon that about 8-10000 lbs was reversed. Thats a lot.
When we got the 737-400 with the CFM engines at 24000 lb thrust, we reckoned we were reversing about half the jet flow through cascades, but the main fan is not reversed and that is a big component. So we reckoned that the -400 was far inferior to the -200 in stopping power under reverse and so it proved to be.
Of course all of this is taken into account in landing performance so even the RJ with no reversers can still land!! But it is severe limited on icy / slick runways where the brakes do very little and the reversers become the dominant retarding force.
R Guy

[retired guy]

Why wouldn't you want to use at least idle reverse?

Hi Flying Stone
You wouldn't is the short answer. Lots of cons and no pros!
R Guy

[retired guy]

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?

This is a thorny annual Centaurus but has been well discussed.
My understanding is this. But note, my understanding!
The thing you are trying to avoid by cancelling reverse, or more correctly going to reverse idle at 60 knots IAS, is the reversed airflow being projected forward and being re-ingested by the Fan Section and causing instability in engine performance and FOD damage. Otherwise you could keep reverse to a standstill. And every now and again I see that as a passenger when the pilot forgets, with the resultant bang as the engine surges.
Now this is all based on IAS , and GS is entirely irrelevant. The airflow felt by the plane is the relative wind which is a combination airplane forward motion and actual wind.
Say landing in 60 its HW you will be canceling reverse as the plane comes to a physical stop (if you wanted to) but the engines are still feeling that same 60 kt relative headwind so the reversed airflow is still not reaching the front of the engine. And no danger of FOD or surge even though the plane is physically stopped.
Take an extreme example. Light plane and 100 kt headwind. You get airborne at 120 IAS with 20 GS. Reach 50 ft and then abort. Then land immediately at 120 IAS GS 20. You could clearly blast away on your reversers to full reverse until the IAS reaches 60 before you would have a problem.
Not sure if that makes sense.
Best wishes
R Guy

[FlightDetent]

Take an extreme example. Light plane and 100 kt headwind. You get airborne at 120 IAS with 20 GS. Reach 50 ft and then abort. Then land immediately at 120 IAS GS 20. You could clearly blast away on your reversers to full reverse until the IAS reaches 60 before you would have a problem.
Not sure if that makes sense. it is not approved to reverse the A/C (negative GS) with reverser use. :E

[retired guy]

it is not approved to reverse the A/C (negative GS) with reverser use. :E
You got there before me Flight Detent. Was just composing correction!
Clearly in that very unlikely situation, which was purely illustrative, you would have to be going backward to achieve 60 kts IAS. But that was not really the point which is that it is IAS that governs the point at which you go from full reverse to reverse idle.
That said we did reverse back in Berlin for a period to evaluate not using the pushback vehicles. It didn't catch on due to the number of broken windows in then terminal due to FOD being thrown forwards but it works!
And I have used it when we were not near any buildings or people on a clean surface (while it was still permitted in the Vol 1 Manual.
Thanks for picking that up.
R Guy

[retired guy]

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. .


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. 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.

Some operators prefer to have the PNF operating the reverse levers on all landings - dry or slippery.
UNQUOTE
Which is why I guess some operators don't let PNF anywhere near the reversers!
R Guy

[ImbracableCrunk]

This may be a good time to point out that Boeing's own FCTM has the wrong thrust levers depicted in this section. Maybe it's the same 767 that they used in the body-contact depictions.

[Busserday]

come on gang. I know that SOPs have become pedantic but fly areoplanes not simulators and for the newbies sweat flap speeds and think about where you are when you cancel the reverse. If your being called by the checker for idiotic definitions think about what reference is needed for the environment. If you have a 60 kt headwind you probably can stop without using much reverse so what are you thinking about?

[Skyjob]

come on gang. I know that SOPs have become pedantic but fly areoplanes not simulators and for the newbies sweat flap speeds and think about where you are when you cancel the reverse. If your being called by the checker for idiotic definitions think about what reference is needed for the environment. If you have a 60 kt headwind you probably can stop without using much reverse so what are you thinking about?
Agreed with technicality, but stick to the unlock of reverse thrust to negate the forward thrust vector in all cases, no need to deploy them beyond that. Saves, noise as at low idle, less then forward idle, reducing noise, too...

[tdracer]

That's it Skyjob
Crank it up to full reverse especially at high speed say >100 its and it really kicks in. Much more effective at high airspeeds hence the need to select right after touchdown. the 737-200 which could reverse almost the entire jet flux being low by pass, using giant buckets, and could stop on reverse alone in about 1800 metres. Landing in Jersey on a wet runway at 1650 metres it was a godsend.
Many of the later High By Pass engines seem to just be big noise machines but even so you are probably reversing 40% of the max thrust - just an estimate. Review any good video of reverse in operation on a wet runway during testing and you can see it is still a big player.


Few reversers do better than about 25% effectiveness - but as noted getting them out early is a big benefit due to the ram drag of all that air going in the inlet at higher speeds. Very early high bypass engines (JT9D/747) had core exhaust 'spoilers' - they didn't really reverse the core exhaust but pretty much eliminated the forward thrust component. However keeping the actuators and such working in the hot exhaust stream was difficult and expensive, and the benefit was minor, so they went away early on.
Most high bypass reverse systems limit N1 to around 80-85% - above that the forward core thrust increases faster than the reverse fan thrust, so there is no benefit to going higher.
The theoretical benefit of not using the reversers is it saves the wear and tear of the deployment actuators and related mechanism (MTBF of a reverser is in the 5000 cycle ballpark). That being said, back during the initial 777 development, I'd just been involved in the Lauda crash investigation (one of the most difficult, painful things I did during my career), and I semi-seriously asked the question 'why don't we just get rid of the reversers' - it was a lot of weight and complexity, they were potentially dangerous, and we didn't get any direct cert credit for them. I was told that on a 777 sized aircraft, using reversers saved ~$100/landing in brake wear and maintenance...