Allegiant MD-83 Elevator Failure
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Allegiant MD-83 Elevator Failure
A report on Bloomberg today details an apparent elevator failure during takeoff on an Allegiant flight 483 from Las Vegas to Peroia, Illinois last week. It appears the plane started rotating early without pilot inputs, leading to a rejected take off. It sounds like possible shades of Air Alaska 261. Here is the link to the Bloomberg article.
Out-of-Control Takeoff Try by Allegiant Jet Spurs FAA Probe - Bloomberg Business
Out-of-Control Takeoff Try by Allegiant Jet Spurs FAA Probe - Bloomberg Business
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Allegiant said an inspection found that a device that moves one of the plane’s two elevators had become disconnected.
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"A preliminary investigation found that a nut on a component that moves the left elevator had fallen off, causing the control surface to become jammed in the up position."
The airline reported the left elevator boost actuator of N407NV had become disconnected. A fleet wide examination of MD-80 aircraft was conducted with no further anomaly found."
The airline reported the left elevator boost actuator of N407NV had become disconnected. A fleet wide examination of MD-80 aircraft was conducted with no further anomaly found."
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Control surface freedom of motion check
If one of the elevators was jammed in the trailing edge up position that must have occurred during the pre-flight freedom of motion check. One would hope that such a failure would be noted during the walk around. During and following the freedom of motion check does the flight crew have feedback as to the actual control surface positions to check for a failure like this?
The article linked speaks of "lift-off". Clearly this event involved pre-mature rotation with the main gear still on the ground. I wonder how close they got to a tail strike? We would have to know the weight, but does anyone have an idea how close they were to Vmu?
The article linked speaks of "lift-off". Clearly this event involved pre-mature rotation with the main gear still on the ground. I wonder how close they got to a tail strike? We would have to know the weight, but does anyone have an idea how close they were to Vmu?
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Elevator Power Check
If one of the elevators was jammed in the trailing edge up position that must have occurred during the pre-flight freedom of motion check. One would hope that such a failure would be noted during the walk around.
On the MD-80 the elevators are checked first by pulling the control column full aft, then by pushing the control column fully nose down until the hydraulic augmentation (Elevator Power) light turns on.
It may be that one of the elevators jammed up during the first part of this procedure -- I don't know how the Elevator Power light is activated to see if this is a possible failure mode.
(The elevators move in response to relative headwind so they cannot be checked for movement prior to taxi).
"…a nut on a component that moves the left elevator had fallen off…" really doesn't provide much info at this point. It could've been any number of components.
Just as a basic anatomy lesson on the MD80 series, the elevators themselves are control-tab operated and not connected to the control columns…or each other. At the gate, it's normal (if the wind is from the tail) to see one elevator in the UP position and the other in the DOWN position.
The only hyd source to the elevators is the elevator augmenter system which isn't a normal operating mode but rather a deep stall recovery effort which uses hyd pressure to push both elevators full down if the control tabs are moved beyond a certain amount in the ANU direction. The ELEVATOR PWR ON light comes on to indicate that hyd pressure has been applied to the elevators…not where the elevators went. This light is observed during the normal control check during taxi by pushing the control column full ANU. This will normally move both elevators ANU which cannot be seen by the crew during taxi. The system has an accumulator so it can move the elevators at the gate if you're inclined to play with it to see it work.
There is no flight control position indication in the cockpit (other than stab trim position) like some airplanes have.
As for the Allegiant situation, the crew wouldn't have been able to see anything abnormal on a walk-around. Before castigating the crew, it might be prudent to wait for a lot more information about this.
I have no idea what would've happened if they'd taken the airplane into the air with one elevator jammed full ANU.
Just as a basic anatomy lesson on the MD80 series, the elevators themselves are control-tab operated and not connected to the control columns…or each other. At the gate, it's normal (if the wind is from the tail) to see one elevator in the UP position and the other in the DOWN position.
The only hyd source to the elevators is the elevator augmenter system which isn't a normal operating mode but rather a deep stall recovery effort which uses hyd pressure to push both elevators full down if the control tabs are moved beyond a certain amount in the ANU direction. The ELEVATOR PWR ON light comes on to indicate that hyd pressure has been applied to the elevators…not where the elevators went. This light is observed during the normal control check during taxi by pushing the control column full ANU. This will normally move both elevators ANU which cannot be seen by the crew during taxi. The system has an accumulator so it can move the elevators at the gate if you're inclined to play with it to see it work.
There is no flight control position indication in the cockpit (other than stab trim position) like some airplanes have.
As for the Allegiant situation, the crew wouldn't have been able to see anything abnormal on a walk-around. Before castigating the crew, it might be prudent to wait for a lot more information about this.
I have no idea what would've happened if they'd taken the airplane into the air with one elevator jammed full ANU.
"…a nut on a component that moves the left elevator had fallen off…" really doesn't provide much info at this point.
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IF you do the hydraulic ram check at the gate, you can watch the reflection of the elevators moving in the glass of the terminal.
It is the norm to push full forward on the yoke as you take the runway to confirm hydraulic ram is working and to equalize the elevators.
It is the norm to push full forward on the yoke as you take the runway to confirm hydraulic ram is working and to equalize the elevators.
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I have flown on Allegiant round trips between Peoria and Phoenix. Never again. I'm not an aviator - just somebody that pays the freight. Poorly managed and not passenger friendly. Are they unsafe? I can't say, but seeing how they manage their operation and the attitudes of many of their employees, I'm skeptical.
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This light is observed during the normal control check during taxi by pushing the control column full ANU. This will normally move both elevators ANU which cannot be seen by the crew during taxi.
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Elevators, operation thereof
AIUI, bafanguy has it 'spot on'.
The elevators respond to the trim tab, not the control column at rest and a ground walk-around won't help you.
Regardless of whether this was a nut that dropped off or a worn jack screw as in the Alaska Airlines accident, this is 100% a maintenance problem.
Damn good job by the flight crew. Without a RTO this jet would now likely be a smoking hole in the ground.
Beware of low cost operators and/or bad management ( how do you know you might ask about management standards ? ). 'Something' is likely to suffer. I hear anecdotally that Allegiant flight crew have a good reputation but what would have happened in the case of another operator ? I believe that the FAA has a duty in this case to inspect MX records for their entire fleet.
The elevators respond to the trim tab, not the control column at rest and a ground walk-around won't help you.
Regardless of whether this was a nut that dropped off or a worn jack screw as in the Alaska Airlines accident, this is 100% a maintenance problem.
Damn good job by the flight crew. Without a RTO this jet would now likely be a smoking hole in the ground.
Beware of low cost operators and/or bad management ( how do you know you might ask about management standards ? ). 'Something' is likely to suffer. I hear anecdotally that Allegiant flight crew have a good reputation but what would have happened in the case of another operator ? I believe that the FAA has a duty in this case to inspect MX records for their entire fleet.
Last edited by Design Engineer; 28th Aug 2015 at 02:56. Reason: addition
peekay4,
"The light comes on when the control column is pushed full forward (nose-down). It should NOT come on when the control column is moved full ANU."
You are quite correct...should've been "AND" Thanks for catching my typo. (haste makes waste !!)
"The light comes on when the control column is pushed full forward (nose-down). It should NOT come on when the control column is moved full ANU."
You are quite correct...should've been "AND" Thanks for catching my typo. (haste makes waste !!)
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I wonder, as a non-pilot, how they were able to get the nose back down in order to reverse the rotation, if one of the elevators was stuck NU. Or....wouldn't the airplane have been asymmetric? Sounds as if this was very near to a bad crash. If this is a stupid question, I can live with that.
how they were able to get the nose back down in order to reverse the rotation, if one of the elevators was stuck NU.
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how they were able to get the nose back down in order to reverse the rotation, if one of the elevators was stuck NU.