View Full Version : B737 - Manual Reversion

ATR Newby
17th Apr 2004, 14:45

I am interested in knowing the forces that are required to move the control surfaces of the B737 during flight in manual reversion, i.e. total loss of hydraulic systems A & B.

In other words, how many pounds of pressure is it necessary for the pilot to apply?


17th Apr 2004, 15:35
(a) I've never taken a measurement but the loads are qualitatively high

(b) .... unless you cheat a little in roll by leading with a touch of rudder

(c) I've had slips of girls in the simulator do it just fine so I guess that makes me a 95lb weakling ...

(d) so long as you have your Weeties for breakfast, it all works out after a little bit of practice.

Seriously, though, it is like pushing against a restriction in an hydraulic damper .. you can push as hard as you like but it doesn't go any faster. If you apply enough load to move the control and then have a little patience, the real loads are not all that high.

Main problem is time delay .. while the powered aircraft is a delight to pole, in manual you really do need to plan ahead and lead early with control inputs.

ATR Newby
17th Apr 2004, 19:13
Thanks for the info - most reassuring :D

However, if anyone has any actual numbers, they would be most appreciated...


18th Apr 2004, 05:55
Those numbers would probably vary depending on airspeed. The aircraft has balance tabs/panels designed to minimize the loads during manual reversion.

Flight Detent
18th Apr 2004, 10:36
Hi all,
and don't forget guys, you also have to manually position the controls back to neutral after the maneuver is complete, they do not automatically return as with power controls.

In the '73, the ailerons are just as hard to push back towards neutral, anticipation is certainly required.


Notso Fantastic
18th Apr 2004, 12:01
I'm physically strong, and I fouond Manual Reversion in a 737-200 about as physically demanding as I could take. The control forces are very, very high and the feel and lack of return to neutral make it extremely demanding. In a real situation, I would say there were significant odds on the aeroplane not surviving the landing.

18th Apr 2004, 12:09
I have to agree with NSF, having been P2 for a test flight in a 737-200 in the mid 1990's where we had to switch off the hydraulics. The control loads from memory were at least as great as in the simulator and I found it almost impossible to do a level turn - seemed to go down at about 700fpm. As NSF says, unless you are given a CAVOK/ light winds with a long straight in approach, expect a tough time and at best a rough landing.

Some people seem to think that the loss of either the A or B systems is ok and you don't need to land at nearest suitable airport as you still have 2 systems remaining - well not me, get it on the ground and argue the toss afterwards.

19th Apr 2004, 08:37
I have checked the B737-600/700/800/900 Aircraft Maintenance Manuals,they do not list a max column force during manual reversion ops or during the manual reversion flight test,all the AMM list is that all forces should be equal (IE left aileron force=right aileron force,ect).
I have listed the MAX Hydraulic Power On Forces for the control inputs.NOTE that all these figures include the use of special adapters between the Column/Pedals so the figures listed are readings from the equipement,NOT THE ACTUAL FORCE APPLIED BY A HUMAN OPERATING THE SURFACES
Aileron force 19 foot-pounds
Elevator 55foot-pounds
Rudder 82foot-pounds

Hope this helps,


19th Apr 2004, 15:20
I have to respectfully disagree with NSF and TB, although my experience is on a NG 737 (which may be greatly different from the -200, and if so, my apologies)

I am a very average-built person, i.e., not terribly strong at all, and I don't find manual reversion to be too bad. I think there are a few things you have to immediately get your mind around, accept, and start doing straight away, if you are in a manual reversion situation.

1) TRIM TRIM TRIM - If elevator trim were ever important in an aircraft, this is certainly the time. If you can minimize the amount of brain cells and muscles you're spending on elevator forces, the yoke gets much more manageable. Remember to re-trim and re-trim as airspeed changes (see B73567AMT's post). With a few practices in the sim recently, both my training partner and I were able to trim "mostly hands-off" in terms of the elevator, and fly the ailerons and remainder of the elevator inputs with a very light touch. But the next two points are key as well:

2) ANTICIPATION & PATIENCE - Expanding on what John Tullamarine said, you have to speed up your crosscheck a bit, in order to anticipate the next-required control inputs. Try to think in terms of "fix it early, with small inputs", rather than waiting until the required correction is large. If you can stay in the "early, small" corrections mode, you can avoid feeling the need to drive the yoke, elbows and all, through its entire range of motion (exaggerating a bit there, but you get what I mean ;) )

3) MAKE A CONTROL INPUT, TAKE IT OUT - That covers what Flight Detent is talking about, with the controls. Hopefully you've got the elevator trim thing sorted by now, but you notice you're starting to drift a little right of course? Put in left aileron NOW (following point 2), and as soon as you get a response, take it out NOW. Almost thinking in terms of short, small "punches" of the ailerons -- just enough to get deflection and movement, but not overdoing it, and then taking that deflection out.

I don't disagree that landings will be sporty--they will. But they don't have to be dangerous at all; in fact you can often get a reasonably smooth landing. Next time you're in the sim, time permitting, ask to do an approach or two with manual reversion, and really try to apply the above techniques. You'll find that when you finally reach the runway, you won't be as physically (and mentally) drained, you're as "in trim" as possible, you're "warmed up" putting in the required inputs with light/early controls, and it's much more manageable in the landing phase. Give it a go and see how it works for you.

ATR Newby - to go back to your original question - as you can see, the amount of control force (in numbers) can't really be measured as a constant, because if you're trimmed up as much as possible, the amount will be less, but if you're not, or when you're making large power changes, etc, the amount will be greater. I've seen pilots (much better than I am) fly manual reversion with a light touch of the fingers most of the time (they are who I got my techniques from) -- I've also seen pilots fly manual reversion with fully flexed muscles, white knuckes, veins exploding out of their forehead, and such. How YOU personally fly has a great effect on the amount of control force required.

20th Apr 2004, 15:42

Have you flown manual reversion in the aircraft or just in the sim?

I agree with you that trim is vital, but flying a turn will result in a descent unless the other pilot trims it - one person cannot do both - certainly in a -200 - believe me!

20th Apr 2004, 16:15
From the AFM:

With the loss of both hydraulic systems A and B, the ailerons are controlled
manually. High control forces are required for turns and the control wheel
must be forcibly returned to the aileron neutral position. Bank angle should
be limited to 20 degrees maximum. Because the rudder is powered by the
standby hydraulic system, it is still very effective, and care must be used to
prevent overcontrol. The elevator is controlled manually; a noticeable dead
band exists. To minimize the effect of the dead band, the aircraft may be
trimmed slightly nose up and a light forward pressure held on the control

The crosswind capability of the aircraft will be greatly reduced. Fly large
landing patterns, with a long straight-in final approach. Keep thrust
changes small or slow to allow for pitch trim changes. Landing
configuration and approach airspeed should be established in-trim on a
level flight path and on the runway centerline so that only a slight reduction
in thrust is required to establish the landing profile. Fly a normal landing
profile. Do not make a flat approach.

For go-around, apply thrust smoothly and in coordination with stabilizer
trim. Rapid thrust application results in maximum nose up pitch forces.
Keep thrust and flight control movements smooth and moderate.
On touchdown, thrust reverser operation will be slow. Apply steady brake
pressure. Do not modulate the brakes. Because of inoperative nose wheel
steering and limited capacity of brake accumulators, do not attempt to taxi
the aircraft after stopping.

ATR Newby
20th Apr 2004, 18:09
My thanks to everyone who has contributed to this topic - your comments are greatly appreciated...

If anyone has even more to add, that would be just great...

Dare I now ask for comments along similar lines for a "jammed control" situation, however hypothetical?

I believe this can require maximum effort from both pilots. (Hopefully applied in the same direction :D )

20th Apr 2004, 19:59
The 737 (NG versions, at least) have some reasonably decent features for jammed controls. We have procedures for these conditions, and practice them routinely in the sim. Not having my books with me at the moment, I'll do my best to summarize:

If it's a jammed roll control (ailerons or spoilers), there's a transfer mechanism which allows one of the yokes (control wheels) to work the operative control. For instance, if the ailerons are jammed, you can move the FO's yoke and roll the acft using spoilers. If the spoiler system is jammed, you can move the Capt's yoke to roll the acft using ailerons. (In each case, the opposite yoke won't move.)

If it's a pitch control (elevator or horizontal stablizer) that's jammed, there are procedures for each as well, but it's a bit different from the roll situation. The elevator has a transfer mechanism between yokes. If it's a stabilizer problem, you have to first determine whether it's really jammed, or whether it's just not responding to one type of input (since it will take inputs from the manual stab trim wheel, the electric trim system, and the autopilot trim system). If it's truly jammed, then yes, it may take great effort to fly, especially as airspeed changes. One technique is to fly the aircraft as close as possible to it's trimmed airspeed (i.e. where it's stuck) as long as is reasonable. That way, when it's time to land and you really need to fly it with as much precision as possible, you and your fellow pilot won't be completely worn out. Again, being a "average-built" pilot, I was able to cope with this reasonably well during my training. It was tiring, and I really had to work at it, but it certainly wasn't impossible.


Re the previous question: No, I've been fortunate so far, and have not had to fly with manual reversion in the aircraft; only in the sim. However, I've just had a word with one of my colleagues, a Boeing test pilot with extensive manual reversion experience in the actual aircraft, to see if there are significant differences between the -200 and the later series. He said that the NG 737s were better by design, when it comes to manual reversion. However, he also said that manual reversion in the earlier versions, including the -200, is (and these are his exact words) "easy once you know how". Of course he's had a LOT of practice, so it would be easy for him. Not so much for the rest of us, but it does lend credence to the fact that technique plays a huge part in these conditions.

He also said that our simulators (the ones our company uses --he's flown them too), fly almost identically to the aircraft and what we're feeling under manual reversion in the sim should very well replicate what we'll get in the aircraft.

21st Apr 2004, 02:17



Elevators +31 lbs will cause breakout
+100lbs will cause 4 degrees of elevator travel

Rudder +18lbs will cause breakout

I can`t find all of the figures as depending on the degree of jam as to what happens.

If you have a RATE JAM (one pogo on a aileron PCU you need +20 lbs for the other pogo`s to drive the PCU`s).

IF you have One Aileron jam ,THE SHEAR RIVETS AT THE BOBY QUADRANT WILL SHEAR AND ISOLATE THE JAMMED AILERON.The other part of the aileron system operates normally.(should be relatively low forces)

If the RH control wheel cannot move ,the crew can only use the left control to move the ailerons (the crew will need to overcome the spring torsion with-in the Aileron Transfer Mechanism and the Aileron Spring Cartridge to isolate the aileron system from the Flight Spoiler System,which should be relatively high forces).

If the LH control Wheel cannot move,the crew can only use the right control wheel.This will move the right body cables after 12degrees of control wheel movement.This controls the flight Spolier Actuators to move ,again(the crew will need to overcome the spring torsion with-in the Aileron Transfer Mechanism and the Aileron Spring Cartridge to isolate the aileron system from the Flight Spoiler System,which should be relatively high forces).

Regards DDG

Burger Thing
21st Apr 2004, 03:36
I just had my last COT a few weeks back. We also practised manual reversion. I tell you, I am about 92 kg, 190m and I couldn't handle it on my own. Thank goodness my FO is into Body Building and we had to put maximum efforts in. It felt like we were steering an oil tanker with wings.

I go with Notso Fantastic about the odds... Hopefully I will never have one...

21st Apr 2004, 05:14
That Transfer Mechanism iis present on the B737 Classic aircraft as well.

22nd Apr 2004, 13:59
Not difficult at all, IMHO!

Just practiced one in the sim (300) yesterday.

Probably in trouble are those who never disconnect a thing in everydays life...:yuk:

If you are good at hand flying, you also know that the secret is the use of trim.

Just trim it so as to relieve any force needed at all time.

I'm afraid those who opt for the no-trim technique in a turn (keeping the force applied troughout the entire turn) start with the wrong foot here also!:p


When you are really good at hand flying, once again, it's like an Airbus, even in a manual reversion!:p

Ignition Override
24th Apr 2004, 07:20
A-300 over Baghdad!

Those who have flown in such a test or real situation can better appreciate those two pilots in the DHL A-300 in Iraq who had no hydraulics and no manual reversion-but did they have any help from the elevator or aileron trim?:ugh:

The DC-9 never required hydraulics for primary controls, so I've wondered why Boeing needed hydraulics for such a jet which is about the same size, without a fairly easy back-up system. Were they simply planning for much larger stretched series?

chuck yeager
27th Apr 2004, 17:40
I am interested in knowing the forces that are required to move the control surfaces of the B737 during flight in manual reversion, i.e. total loss of hydraulic systems A & B.

In other words, how many pounds of pressure is it necessary for the pilot to apply?

The following may or may not be relevant :

FAR 25.143 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&rgn=div8&view=text&node=14: :

FAR 25.143

Controllability and Maneuverability

25.143 General.

(a) The airplane must be safely controllable and maneuverable during—

(1) Takeoff;

(2) Climb;

(3) Level flight;

(4) Descent; and

(5) Landing.

(b) It must be possible to make a smooth transition from one flight condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane limit-load factor under any probable operating conditions, including—

(1) The sudden failure of the critical engine;

(2) For airplanes with three or more engines, the sudden failure of the second critical engine when the airplane is in the en route, approach, or landing configuration and is trimmed with the critical engine inoperative; and

(3) Configuration changes, including deployment or retraction of deceleration devices.

(c) The following table prescribes, for conventional wheel type controls, the maximum control forces permitted during the testing required by paragraphs (a) and (b) of this section:

Force, in pounds, applied to the control
wheel or rudder pedals Pitch Roll Yaw
For short term application for pitch and roll 75 50 .......
control_two hands available for control.....
For short term application for pitch and roll 50 25 .......
control_one hand available for control......
For short term application for yaw control... ....... ....... 150
For long term application.................... 10 5 20

ATR Newby
28th Apr 2004, 00:03
Surely not THE Chuck Yeager???

In any case, I am most grateful to everyone who has contributed to my topic - gentlemen, all your answers have been of inestimable value to me - I thank you all once again :ok:

28th Apr 2004, 02:44
Next time you land it nicely in the simulator during manual reversion and get that warm inner glow (it's happened to me), ask the sim instructor to IP you back to about 2000 ft with some mild wind shear and turbulence and then see how easy it is.

By mild wind shear I mean a change in wind speed of say 10 kts and 30 degrees over 2000 ft with just some light chop. Nothing that you wouldn't experience on a fine sunny day.

I have seen one guy get it nicely to the flare, and then dig a wing tip into the ground and lose it completely. It all happened very quickly.

Our sim instructor had already advised us that from what he's seen, it'd be a good idea to perhaps get the cabin prepared for a possible evacuation incase you should ****** it up.

I remember thinking that that was probably over doing it and would only freak out the passengers unnessesarily. But after seeing this guy lose it in the flare so easily, I think I might take that advice after all if I should ever find myself flying on manual reversion for real.

We were flying the B737-400 simulator.