About Wing Twist

[AlphaMike]

I am a new member from Europe, so I ask you to be indulgent with my English.

My question is about wing twist by ailerons that may occur in flexible wings airliners.

As far as I know, airliners are equipped with spoilers that work in conjunction with the rising aileron. This provide additional drag and downwards force that tend to help the aileron. The spoilers’ deflection limits the need of aileron deflection. A fully deflected aileron can twist the wing and provide an opposite movement then what intended by the pilot.

My question is: what happen if the device that coordinates the aileron and spoilers fails and the aileron rises without being “helped” by the spoilers? Is this really problematic? Can this leads to reversal control situation?

Thank you for your help!

[Denny of Oakland]

Most ailerons and spoilers are not so independent of each other. However it will depend on the aircraft you are referring to. Most aircraft have computer inputs that will prevent this type of action from happening. On the larger aircraft they have feel and trim inputs that take inputs from the back up systems. Most aircraft will have three hydraulic systems that feed thru what is called a feel and trim unit.

The feel and trim takes inputs from the aileron power package, trim centering and feel unit and sends a signal to the computer that tell the system what to do. If a spoiler or aileron goes off line from hydraulic system 1 it will shift to the back up system hydraulic system 2 or 3 depending on the design.

There are shut off vales in the system to prevent a spoiler from rising on it’s own controlled by the spoiler mixer unit and ailerons will have lockout mechanism, which is a safety device.

The pilot will get a light in the cockpit from the transfer valve indicating a problem, which feed thru the aileron programmer.

Sorry the detailed stuff as I am a maintenance type.

Denny of Oakland

[AlphaMike]

Thank for your reply Denny.

I am referring to airplanes as the Boeing 737-300. Generally speaking airliners with not necessarily huge wings but with sufficient flexibility.

There is an ailerons/spoilers hydraulic mixer. I wonder what could happen if this mixer doesn’t work. The ailerons will still work, but without the spoilers. As far as I know, when the aileron is fully raised the flight spoilers are fully deflected on the side of this raising aileron. These spoilers (2 on the 737-300) add a considerable force to roll the airplane.

For me, if the aileron is completely deflected towards its upper course, it can introduce a sufficient moment to twist for some degrees the part of the wing where it’s located. This twist can increase the incidence of the wing and therefore increase the lift. The wing will go up (the expected movement was downwards).

Please see attachment. In the image, the movement is exaggerated a bit.

Thank you !!!

[Denny of Oakland]

I will need a few days to go over the 737-300 flight control system. After a review I will be able to answer your question better. However the question I have is why are you interested the flight control system of this peculiar aircraft?

Denny of Oakland

[Denny of Oakland]

Amine,

I have checked the AD listing on the 737-3Q8 in question and have found several problems with the aileron control system that can or could be fixed to prevent a problem from happening. The aircraft that crashed is a high time aircraft of unknown maintenance being performed. There is very little data I can find on this aircraft.

However, if the required maintenance was not performed anyone of the following AD’s may cause a accident like this. Knowing if the AD’s had been complied with would make your search much easier. All the AD’s can be found at www.faa.gov search under AD listing for large aircraft and type in the make and model you will find a complete list. However without the maintenance records you would not be able to tell which ones are complied with.

Below is some of the information I did find to aid in your search:

Boeing 737-3Q8
Operator; Flash Airlines
Built 1992
Total airframe hours: 25592
Cycles 17973
Aircraft Serial number: UNKNOWN

Boeing AD listing

AD 2002-18-02
To prevent jamming of the first officer's control wheel due to the presence of a foreign object on the lower bearing support of the transfer mechanism for the aileron, which could result in reduced controllability of the airplane.

AD 2000-02-18 C
To prevent a reduced rate of movement of the elevator, aileron, or rudder, which, if not corrected, could result in reduced controllability of the airplane.

Model 737-100, -200, -300, -400, and -500 series airplanes; certificated in any category; equipped with: a rudder power control unit (PCU), having part number (P/N) 65-44861-( ), P/N 65C37052-( ), or P/N 65C37053-( ), except those having a serial number of 1252A or greater or having a serial number that contains "ss"; or an aileron or elevator PCU having P/N 65-44761-( ), except those having a serial number of 5360A or greater or having a serial number that contains "ss."

Compliance: Required as indicated, unless accomplished previously.
To prevent a reduced rate of movement of the elevator, aileron, or rudder, which, if not corrected, could result in reduced controllability of the airplane, accomplish the following:
PARTIAL RESTATEMENT OF REQUIREMENTS OF AD 97-09-14:
(a) Within 5 years or 15,000 flight hours after June 6, 1997 (the effective date of AD 97-09-14, amendment 39-10010), or at the next time the PCU is sent to a repair facility, whichever occurs first: Perform an inspection of aileron and elevator PCU's having P/N 65-44761-( ), except those having a serial number of 5360A or greater or having a serial number that contains "ss"; and rudder PCU's having P/N 65-44861-( ), except those having a serial number of 1252A or greater or having a serial number that contains "ss"; to determine whether a PCU manifold has a reworked or repaired cylinder bore(s) containing chrome plating. Accomplish this inspection as specified in paragraph (a)(1), (a)(2), or (a)(3) of this AD.
(1) Inspect the airplane maintenance records to determine whether a PCU with a chrome-plate-repaired cylinder bore is installed. If inspection of the maintenance records shows that the PCU meets one of the criteria specified in paragraph (a)(1)(i), (a)(1)(ii), (a)(1)(iii), or (a)(1)(iv) of this AD, no further action is required by this AD for that PCU.
i)The PCU has never been reworked or repaired.

Incorporation by Reference
(i) The PCU NDT shall be done in accordance with Boeing Service Letter 737-SL-27-120, dated January 28, 1998. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., Suite 700, Washington, DC.
(j) This amendment becomes effective on March 9, 2000.

AD 2002-10-12
To prevent a disconnected aileron tab, which could lead to severe airframe vibrations; consequent damage to the aileron tab, aileron, and wing; and loss of controllability of the airplane.

AD 99-25-02
To prevent the linkage between the ratio changer input rod and the aft aileron control quadrant from becoming disconnected, which could result in reduced controllability of the airplane.

AD 99-10-12
To detect and correct corrosion and cracking of the actuator beam arm of the main landing gear (MLG), which could result in damage to the control cables of the aileron and spoiler and consequent reduced controllability of the airplane.

AD 98-03-09
To detect and correct defective ailerons installed on the airplane, which could result in in-flight separation of an aileron from the airplane and consequent reduced controllability of the airplane.

AD 97-05-09
To prevent reduced roll and/or pitch rate control of the aileron and consequent increased pilot workload.

AD 97-04-01
To prevent jamming of the aileron control system during flight, which could result in reduced lateral control of the airplane.

AD 97-03-14
To prevent fatigue cracking or fracturing of the pulley brackets, which could result in slack in the cables and consequent reduced ability of the flightcrew to control the aileron.

AD 80-07-02
To detect a control valve which could cause control surface reversal, within three days from the effective date of this AD, unless already accomplished within the last 14 days, conduct a one time manual input hardover test on the flight control system.