Blackbird From , joined Dec 1969, posts, RR: Posted (11 years 4 months 1 week 4 days 7 hours ago) and read 4424 times:
Most aircraft have a locking mechanism on the flaps to hold them down against aerodynamic forces should hydraulics fail.
The DC-10 relies just on trapped-hydraulic fluid.
Does the MD-11 have a locking mechanism, or does it use the same type of trapped-hydraulic-fluid system.
Basically, the question is: If the MD-11 suffered a hydraulic failure on takeoff, would the slats retract or would there be a mechanical-locking mechanism to hold the slats down?
With a DC-10, they could retract (I remember reading about that happening in 1979 [AA 191]), I just am curious to know if it would happen to an MD-11 too.
Minuteman From United States of America, joined Aug 2000, 271 posts, RR: 0 Reply 1, posted (11 years 4 months 1 week 4 days 6 hours ago) and read 4324 times:
Good question...it has to be...its already been asked and answered regarding the MD-10 conversion process.
FDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 44 Reply 2, posted (11 years 4 months 1 week 4 days 3 hours ago) and read 4307 times:
The DC10 has 3 mechanical slat actuation assemblys.
Each of these assemblys moves a set of slats via cables (big, heavy cables).
You have:
1) An inboard slat actuation assy located at the aircraft centerline which move the L/H & R/H slats inboard of #1 & #3 engine
2)Left outboard slat actuation assy which moves all slats outboard of #1 engine.
3)Right outboard slat actuation assy which moves all slats outboard of #3 engine
Each of these mechanical slat actuation assys use 2 hydraulic actuators to move the cable drum on these actuation assys which moves the cables which in turn extend and retract the slats (Douglas and their cables).
Normally the slats are extended and remain extended due to hydraulic pressure trapped in the hyd. lines between the actuators on the actuation assy and its respective control valve (one control valve per actuation assy for a total of 3).
With AA in ORD, the catastrophic engine separation severed the lines going to the L/H outboard slat actuation assy causing the airload to retract the L/H outboard slats.
To protect against this possibility from reoccurring, the right and left actuation assys have "balanced relief valve" assys installed. Now, should a loss of hydraulic pressure occur with the slats extended, the balanced relief valve will close locking the respective slats extended by trapping fluid in the actuator regardless of hydraulic line damage. These balanced relief valves are on both outboard slat actuation assys but not the inboard assy(located within the fuselage).
The MD11 has a mechanical locking mechanism as well as the aforementioned balanced relief valves for use in case of mechanical failure of the slat actuation mechanism.
On either aircraft, the slats should remain extended in the event of hydraulic failure.
TEDSKI From , joined Dec 1969, posts, RR: Reply 3, posted (11 years 4 months 1 week 3 days 21 hours ago) and read 4282 times:
Because the DC-10 does not have a slat locking system is what caused AA 191 to crash at O'Hare in May 1979, when an engine tore off the wing and severed the hydraulic lines in the wing causing the slats to automatically retract and cause the plane to roll over.
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