The actuators that move the elevators of a privately operated MD-87 that crashed at Houston Executive Airport Oct. 19 were jammed in the trailing edge down position and that made it impossible for the aircraft to take off. The NTSB preliminary report says the elevator actuators were both bent enough that they prevented the elevators from fully responding to pilot control inputs. “Upon reaching rotation speed, the recorded elevator positions split, but neither moved to a trailing edge up position,” the report says. The aircraft ended up 1400 feet off the end of the runway after the rejected takeoff. All 23 occupants escaped and two were seriously injured. Most of the plane was consumed by a post-crash fire but the tail stayed intact.
The elevators on those types of aircraft are not directly connected to the control yoke. Rather, they are free hinged and moved up and down aerodynamically through the manipulation of small control tabs on the trailing edge. Therefore, there is no way to check the operation of the elevators during the preflight. The report doesn’t say how the actuators that connect the tabs to the elevators got bent but it does draw comparisons to the overrun of an MD-83 in Michigan in 2017. In that incident, the board concluded that the actuators were damaged by high winds while the aircraft was parked. The aircraft in the Houston mishap had reportedly been parked for 11 months and there has been plenty of wind in the Houston area in that time. All the components and recorders are being studied by investigators and the official cause of the crash won’t likely be released for a year or more.
When we (my airplane partner and I) were building our Glasair, after the control stick and its linkages were installed in the wing, I climbed onto the wing jig, and, like a little kid at one of those grocery store nickle machine aircraft rides, I sat in the “plane” making airplane noises and rocking the stick around, as if a fighter pilot.
“Clunk, clunk.” The stick jammed while pulling back into a high G maneuver.
I did what most pilots probably instinctively do in a situation like this in flight. I tried pulling back again, harder, only to have the elevators jam again.
They were not going to move.
It turns out that the (rather largish) cannon connector for our S-Tec autopilot was innocently lying under an elevator bellcrank. Being metal, it was not going to yield. Lesson learned.
While not the same as what happened here with the MD-87, I have ever since been paranoid about anything that could jam the elevators. (Or any control.) The smallest thing can do it.
I used to do GA post-maintenance test flights in Hawaii, and flew trainer vintage warbirds in SE Asia.
Boy, both were eye-openers. Anything that can go wrong, does go wrong. But double that in areas with high humidity or sea-spray corrosion. Aluminum, regardless of thickness, just turns into a paste that you can scratch with your fingernail, so you can’t trust that the flight controls will stay attached to the airframe (I looked at one Aztec in HNL that had gone from airworthy to “needs disassembly and a rebuild” in only a decade.)
I was offered a flight on a DC-3 that had been sitting around for decades, and I was like, “Thanks, but no thanks.”
The MD80 Series has a unique elevator control system, explained so well by Juan Browne on his YouTube:
https://www.youtube.com/watch?v=UTUPGUB8bKQ
The elevator itself is free hinged, and the pilot controls the elevator with control tabs, similar in function to trim tabs on small aircraft. The pilot has no direct control of the elevator, and there is no routine pre-flight check that is free. Only after reaching sufficient airspeed over the control tab would this be functional, even if the elevator would were not jammed. Elegant design, and makes the takeoff roll an act of faith.
Check Boeing 707 elevator system?
Certainly illustrates need to know the frailties of your airplane.
What I am wondering is how come a design that has been in service since the 1960’s is now having difficulty with jammed elevators caused by excessive winds while parked?
Matt, I think this is a situation where the original commercial operators learned to maintain and operate the design safely. Now that the airframe is less common and parceled out to private operators, the safety culture that kept them operating is no longer.
Looks like this is a repeat of the March 8, 2017 MD-83 crash at Willow Run Airport, Ypsilanti, Michigan (AVweb covered it in some detail). Thinking that there needs to be a way to tell if the elevators are jammed on the preflight on the DC-9 series aircraft – right now there isn’t. The control yoke moves correctly because it’s just moving the trim tabs and the crew cannot tell if one or both of the elevators is jammed in position.
There is a limitation on the airplane prohibiting parking it in a tailwind of more than 50 MPH or knots, don’t remember which, but one wonders if the operators remember that bit of trivia.
As a contracted pilot arrives to fly a personally owned aircraft, I suppose the pilot would need a 30 foot ladder to preflight the elevator. Or maybe three ladders and two friends, depending on the counterweighting of the elevator design.
The counterweighting of the elevators is pretty good on the MD-80. They move in the slightest breeze.
Have to study the flight manual, which is voluminous.
Could Douglas have added/changed something to reduce sensitivity of the system to damage by wind?
Just wondering, it is old history by now.
My understanding of the MD-80 series aircraft is limited to the information contained in this article, so I have some questions. Is the control yoke mechanically connected to the elevator actuators (control tabs)? If so, could the jammed actuators be felt in the movement of the control yoke? Is the elevator control tab system separate from the elevator trim tab system?
Yes Robert, the stab trim has an electrically operated screw jack system that moves the leading edge of the stab up & down.
Like the article says, “it may take a year for investigation results”.
Will WE ever see them here???
Well … AVweb reported on the NTSB investigation results on the MD-83 jammed elevator takeoff crash at Willow Run – and noted that the NTSB praised the flight crew for acting correctly in the few seconds they had to recognize the problem and abort the takeoff. It was also interesting to see the detail that the NTSB went into during its investigation into the circumstances of the accident.
There were more than 100 people on that airplane, one person suffered minor injuries – a combination of excellent crew training and good crashworthiness in the aircraft design. Plus, none of the pax tried to take their luggage with them when they evacuated, they followed the cabin crew’s preflight briefing and got out fast even though two of the emergency exits malfunctioned.
The damaged actuators shown are for geared servo tabs outboard of the control tabs. These tab move when the elevators move and are not tied to the controls. The inboard tabs are mechanically hooked to the controls and would have behaved fine prior to being subjected to an aerodynamic load.
Jammed controls discovered while still on the ground at liftoff Vspeeds are incredibly more preferable than 10 seconds after rotation after liftoff with the aircraft rapidly accelerating and several feet above the ground. Those people aboard the accident aircraft were very, VERY lucky.
This airplane had not flown for over 10 months prior to the accident flight due to maintenance. Loading 20 people on an airplane that has down that long for maintenance, routine or otherwise shows a collective lack of aeronautical decision making by the owner and crew. 10 months gives plenty of opportunity for the damage those elevator hinges took due to wind gusts.
Those elevator controls, as others have already pointed out, are finely balanced. Any wind up the tail can make them hit the stops. When in airline service , these airplanes did not sit idle much except for maintenance done in good indoor hangar facilities. And line maintenance kept a keen eye on potential wind damage from local weather or jet blast from other airliners. There was a concerted effort to minimize damage to the Dc-9/MD-80 series airplanes from I have spent several years in a couple of Part 145 refurbishment shops where phase checks, complete paint/ interior refurbs, avionics upgrades, sometimes engine changes are routinely done and could count on my hands the number of post maintenance check flights performed by the owner(s) or contract pilots. 90% show up on the ramp with dogs, kids, wife, mistress , in-laws and outlaws for that first flight in their shiny, leather wrapped Belchfire 10,000 for that first flight after major refurbishment. Often times launching IFR at minimums.
This flight was just another routine flight as far as the owner and flight crew was concerned. That changed when rotation did not happen. In addition, I wonder how and why this flight was a Part 91 flight. I never knew there is a way to fly an airliner under Part 91. Lastly, 6700 feet is not a lot of runway for an airplane if this size. It was amazing the crew got it stopped with the help of the local topography, sheared off landing gear, and stopped in only 1400 feet beyond the end of the runway. I wonder if the NTSB will make a decision on probable cause largely contributed by a total lack of ADM prior to flight.
Airlines publish a flight schedule, and they operate those scheduled flights under Part 121 regulations. But most of the unscheduled flights (test flights, reposition flights, maintenance flights) are operated under Part 91. When an air carrier operates a charter flight (think major-league sports teams), they might do it under Part 135 or they might use Part 121.
My point being, the aircraft type doesn’t really influence the operation type.
Jim, What is ADM?
I imagine that ADM probably stands for “aeronautical decision making”.