A question on B737 manual reversion forces

[Tee Emm]

Volume 2 of the FCOM, chapter 8 Flight Controls says "With total hydraulic power failure the ailerons can be mechanically positioned by rotating the pilot's control wheels. Control forces are higher due to friction and aerodynamic loads"


During my type rating on the 737-200 and after the initial simulator training, a Boeing instructor turned off all hydraulic pumps in actual flight to allow me to get the feel of manual reversion. Of course, hydraulic power was reinstated for the landing. Although it was many years ago, I recall the control forces were high but the aircraft quite flyable.


Since then I have flown many manual reversion approaches and landings in simulators with no serious difficulty. More recently I flew a 737-300 simulator where the control wheel force to use the ailerons on manual was beyond my physical capacity to turn the control wheel more than 20 degrees left or right. It was well nigh impossible to fly an ILS. I don't recall the real aircraft being anything like that which I experienced in the simulator. The stick force in the elevators of the simulator on manual reversion were high as expected but flyable. But the ailerons were bad news.


Very few Boeing 737 pilots would have flown manual reversion in the real aircraft so they would have no experience except in a simulator and that is not often anyway. It then becomes a subjective assessment. It should not require a pilot's full strength to apply the ailerons on a manual reversion. I am interested if other pilots have found marked variation in other 737 simulators in aileron stick forces need to successfully complete a manual reversion approach. For example should you be able to apply full control wheel aileron in manual reversion if required or is that impossible due to design limitations without hydraulic assist?


Another pilot had a go at the same simulator I had trouble with and needed his full arm strength to turn the wheel more than 20 degrees but he did it and was stuffed afterwards! In my view it wasn't flyable.

[Shytehawk]

Is your simulator crook?

[de facto]

In my recent sim,i got manual reversion which wasnt too problematic but indeed required heavier forces to bank but far from impossible.
Using clean speed instead as soon as possible makes all easier as air loads are reduced.
Maybe your sim got you a jammed ailerons in there as well?

[CL300]

Just my 2 cents,
Generally speaking , simulators are just computers with 'triggers' in order to mimic the airplane behavior in some circumstances.
If the checklist calls for green dot for example in order to fly the aircraft without hydraulics, if this first condition is not met, the simulator will not recognize the procedure as per se.
Therefore it is not impossible that following an update of the said software, this specific trigger was misplaced or its tolerance "tighten", making it more difficult to fly.
If the design and certification allows the plane to be flown with the standard control wheel, the forces cannot exceed a published value, laid in CS25 literature.
It is worth a check with the training organization... Humans are human, and do mistakes..

CS 25.671
CONTROL SYSTEMS General
If the functioning of stability augmentation or other automatic or power*operated systems is necessary to show compliance with the flight characteristics requirements of this CS*25, such systems must comply with CS 25.671 and the following:
......
(c) The aeroplane must be shown by analysis, test, or both, to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems) within the normal flight envelope, without requiring exceptional piloting skill or strength. Probable malfunctions must have only minor effects on control system operation and must be capable of being readily counteracted by the pilot.
(1) Any single failure not shown to be extremely improbable, excluding jamming, (for example, disconnection or failure of mechanical elements, or structural failure of hydraulic components, such as actuators, control spool housing, and valves). (See AMC 25.671(c)(1).)

AMC 25.671(c)(1)
Control Systems – General
To comply with CS 25.671(c)(1) there should normally be –
a. An alternative means of controlling the aeroplane in case of a single failure, or
b. An alternative load path.

would be

From CS25.405........IF boeing had chosen the reversion as secondary controls

Control Limit pilot forces
Miscellaneous: *Crank, wheel, or lever.
( 25.4 + R /76.2 )x 222 N (50lbf), but not less than 222 N (50 lbf) nor more than 667 N (150 lbf)
(R = radius in mm). (Applicable to any angle within 20° of plane of control).

That would fit within your hands on experience..

[Lord Spandex Masher]

Very few Boeing 737 pilots would have flown manual reversion in the real aircraft so they would have no experience except in a simulator and that is not often anyway. It then becomes a subjective assessment. It should not require a pilot's full strength to apply the ailerons on a manual reversion. I am interested if other pilots have found marked variation in other 737 simulators in aileron stick forces need to successfully complete a manual reversion approach. For example should you be able to apply full control wheel aileron in manual reversion if required or is that impossible due to design limitations without hydraulic assist?


I've flown in manual reversion about twenty times in the last couple of years. Without fail it has been impossible to apply more than about twenty degrees of hand wheel using one arm (maximum effort with both hands got us to about forty degrees). As far as I know there's no requirement to be able to to apply full aileron, as long as the force required to move the wheel is broadly symmetrical that's a pass.

Sounds like your sim is more accurate than the others. I've always found the sim easier than the real thing in MR.

[JammedStab]

I seem to remember doing manual reversion in the 727 sim. There was a detent with the ailerons neutral and a large amount of a sort of breakout force was required to initially move the control wheel and then a bit less force required for further control wheel movement.

Is this the same on the 737.

[c100driver]

I have also done quite a few manual reversion operation check flights in the B733.

My experience of the "feel" is the same as Lord Spandex! Our simulator is subjectively close to what I have experienced in the real aircraft.

I also had to fly the B732 aircraft as part of my initial conversion in a manual reversion mode due to the simulator being unable to replicate anything like the real aircraft (it was an early three axis model). It was a long time ago now but recall that the B732 was quite reasonable to control and not that heavy, however the 300 does feel a little more ponderous so maybe some of the changes to the wing contour may be a reason?

[Jwscud]

We had a long discussion about this after experiencing manual reversion in the last sim. After 20 minutes in the sim flying on manual reversion taking turns to handle the aircraft we talked about how difficult it would be in the debrief.

The TRE taking our sim was a regular air tester and gave us the happy news the sim was broadly accurate but the forces were in fact higher in the real aircraft (738).

[flying apple]

talked with a colleague the other day and he did fly manual reversion on the real life (on a maintenance test flight, so no emergency) and he said it was easier in real then in the sim (737NG)

[Tee Emm]

Thanks to all for your replies. I have copied them to our simulator technicians who found them most informative.

[aviator1970]

For a manual reversion in a flight check is there a supplementary procedure?

[BBK]

TM

I had a brief go at manual reversion on an air test many years ago on a 737 (300 or 400 can't remember) and subsequently in the sim. From what I recall the forces were broadly similar ie the ailerons were pretty hard to move but it was perfectly flyable on a straight in approach. Hope that helps.

[despegue]

Use the rudder:E