Boeing 737 reverser

[alain-b737]

I would like to know what is the operation of the reversers on the Boeing 737. When you pull on these reversers there is a stop at about 3/4 of the course. But it is possible to overpass this position. What is the use before and after this position? Why is this stop there?
Thank you,
Alain

[Rainboe]

There is a long pull up for the interlock which is idle reverse. You can then pull up more reverse power by pulling further. You come to another interlock. Even more pulling will get you full reverse power.

[alain-b737]

Thank you Rainboe,
Do you know what would be in poucentage (%) the reverse power up to the first step?
I assume that from this first step to the end this is 100% reverse power...!
So why is that first step? Usually do you go completly full reverse every landing???
Many thanks,
Alain

[Rainboe]

First detent is idle reverse. Second detent is a reasonably large reverse power setting. This is set in accordance with engine life considerations. You can go beyond the second detent.

I'm afraid I can't tell you the power settings. One place you are not looking is at the engine instruments!

To give you an idea of standard practice, it is always to select idle reverse. Second detent I have not used in years. Full reverse- not at all on the 737. Reverse power is not very effective, and VERY noisy. It is also very bad for the engine, ingesting debris off the ground, shaking it badly and wearing the translation mechanism. I very occasionally pull beyond the first detent until it gets noisy enough. The autobrake is the main stopping aid. On the 747 with its much larger engine and more complicated reverse mechanism, it was not unusual to have one engine stay in idle reverse with the mechanism unable to travel. you could simply taxi in and leave it like that for the engineers to reset. It was prohibited for the pilots to operate it then in case they caused damage to the mechanism.

[RYR-738-JOCKEY]

On the CFM56-7B-26K you'll get roughly; 1st detent 45%, 2nd detent 70%, full reverse 82%. More interestingly, these reverse N1 figures equate to around 50% reverse thrust of what you can expect of same N1 with "forward" thrust. This varies with speed. The higher the speed, the more efficient the reversers work. At lower speeds the brakes will be far more efficient.
I'd like to add the misconception of pulling hard will give you more reverse and also faster. There's a mechanical lock which prevents deployment above 10' RA, and at touch down you'll first get idle reverse then after successful deployment you may increase all the way to full reverse. Some guys keep pulling the levers till they get their desired reverse. This is not only wrong but may cause damage to the levers. Pull once and deploy them, wait for two seconds with a slight pull and they will click out of the detent at the earliest opportunity.

[alain-b737]

Thank you so much to both of you. :ok:
I have had the chance to obtain real B737-200 throttle for my simulator. On them I can see only 2 detents. Once the throttle handles on iddle position it is possible to activate the reversers. So the first detent (the only one) is at about 3/4 of it's course and left 1/4 to full reverse... So I suppose they are differents from 737NG throttle. I know it is a little different from outside but do not know for the mecanism.
Thank you for your help making my sim as real as possible :)
Sorry for my poor english :cool:
Sim 737NG - ALAIN TREMBLAY - FABRICATION D'UN COCKPIT (http://www.sim-737ng.com/)

[alain-b737]

Thank you so much to both of you. :ok:
I have had the chance to obtain real B737-200 throttle for my simulator. On them I can see only 2 detents. Once the throttle handles on iddle position it is possible to activate the reversers. So the first detent (the only one) is at about 3/4 of it's course and left 1/4 to full reverse... So I suppose they are differents from 737NG throttle. I know it is a little different from outside but do not know for the mecanism.
Thank you for your help making my sim as real as possible :)

[Tee Emm]

To give you an idea of standard practice, it is always to select idle reverse. Second detent I have not used in years. Full reverse- not at all on the 737. Reverse power is not very effective, and VERY noisy. It is also very bad for the engine, ingesting debris off the ground, shaking it badly and wearing the translation mechanism

One presumes you have written to the aircraft manufacturer of your opinions on the use of reverse thrust and recommended to Boeing they change their procedures? Certainly it contradicts the recommendations contained in the flight crew training manual. If you care to compare the effect of reverse thrust when correctly applied, to the stopping distance on a wet, slippery, or contaminated runway versus that of a dry runway you will see a significant benefit.

[HAWK21M]

mechanically the Fwd thrust lever & reverse thrust lever are interlocked mechanically that only one can be moved at a time.

If the fwd thrust lever is fwd the r/T lever will not operate & vice versa.

On the detent part.....Initial R/T lever mvmt is till a particular point through interlocks that prevent further R/T lever mvmt until the T/R sleeves are deployed.Thereafter there are Two detents on the lever itself which provide a mechanical feel to the location when reached.

regds
MEL

[Rainboe]

One presumes you have written to the aircraft manufacturer of your opinions on the use of reverse thrust and recommended to Boeing they change their procedures?

There's always one! It's why I thought whether I should answer at all, but I mistakenly went ahead. I shouldn't have bovvered! The FCTM may state Boeing's recommended operation. This may be amended by operator or airport requirements. Most airports I go to require reverse to be limited to idle for noise and nuisance reasons.

[alain-b737]

HAWK21M,
Your web site is very amaising one. I just discovered it is your site... I know and visit this site since years... :) It is very usefull for those like me who need informations to make their simulator as real as possible.
I invite you and everyone to visite my site on my B737NG cockpit simulator building...
Many thanks,
Alain

[Cough]

I have had the chance to obtain real B737-200 throttle for my simulator. On them I can see only 2 detents. Once the throttle handles on iddle position it is possible to activate the reversers. So the first detent (the only one) is at about 3/4 of it's course and left 1/4 to full reverse... So I suppose they are differents from 737NG throttle. I know it is a little different from outside but do not know for the mecanism.

The -200 only had 2 detents as you have found. The first was idle, the second if you found it would have overboosted the engines (ie. exceeded max TOGA EPR). Max reverse was normally when the levers were vertically up and then trimmed towards the TOGA bug on the EPR gauge.

BUT...Day to day, the -200 reversers you would never use more than about 1.3 EPR (TOGA EPR was just over 2.1 (-15 engines)) as the buckets were so effective.

[DC-ATE]

Rainboe writes:
"Reverse power is not very effective, and VERY noisy."

I don't know what model '37 you're talking about, but you can BACK UP
a -200 with reverse thrust; that's how "effective" they are. Of course, one would never attempt that because of FOD problems but, they are most effective in helping to get stopped if conditions are less than favorable. Or, even in favorable conditions, obviously.

[Rainboe]

Yes, for a brief period we did powerbacks on the 737-200. I didn't like doing them, too much potential for mistakes. Lots of noise for little push. I have always thought reverse power is not very effective in relation to noise and vibration produced. Now most airports in Europe restrict to idle reverse anyway. Autobrake is the effective way to slow down, and you can select what degree you want. Guys that use manual brakes start punishing them on one side only- that matters on a hot day with no wind and short flights.

[despegue]

Reverse is a very useful braking method on slippery runways or when you have a short turnaround combined with short runway (provided noise-abatement procedures allow).
Remember that reverse effectiveness reduces with reducing speed and stow them by 60kts. unless necessary for stopping the aircraft or skidding.

ALso, and that is something a lot of our colleges omit, make sure that both reversers actually work correctly by putting them in first detent immediately after touch-down (remember, they are the most effective when your speed is still high) and only then select the amount you deem needed.
In my opinion, there should be an SOP where the PM calls "Both reversers normal".

Also remember that when you have autobrake selected, putting more reverse will NOT reduce your landing distance, it will merely reduce the brake pressure. (autobrake measures decelleration ).

Despegue

[Rainboe]

stow them by 60kts.
Not right. The instruction is to start reducing reverse power at 60kts and go to fwd idle by 20kts. You should leave them in reverse mode until you are absolutely certain stopping is assured in case of brake failure, so there is no harm in leaving them in reverse idle until 20kts just in case you need them. I find I have to convince several new pilots you should do this as they get very nervous about any reverse below 60kts- they all want to frantically cancel it too early.

[Prop's ????]

You should leave them in reverse mode until you are absolutely certain stopping is assured in case of brake failure, so there is no harm in leaving them in reverse idle until 20kts just in case you need them. I find I have to convince several new pilots you should do this as they get very nervous about any reverse below 60kts- they all want to frantically cancel it too early.

B737 FCTM - "The thrust levers should be positioned to reverse idle by taxi speed, then to full down after the engines have decelerated to idle."

If the brakes have failed you would know well before 20 kts.

Unless every pilot is instructed to do this you will spend you hole life teaching.

[despegue]

Rainboe, that is what I mean, I should have said reduce from 60kts.
If you read my post, I am sure that you notice me pointing out the "stopping assured " condition.

[eagerbeaver1]

738 Jockey - Music to my ears. I reckon I ask at least once a day if the other chap would mind not trying to tear out the reverse thrust levers - you can see them flexing under the strain.

Despeage- We have that SOP - "2 reversers **%" - Works well, especially if the lad is trying to pull both when one is wire locked.