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Air Force: B-52 crash caused by equipment position
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Author:  skymstr02 [ Sat Feb 14, 2009 1:15 pm ]
Post subject:  Air Force: B-52 crash caused by equipment position
A deadly B-52 bomber crash off Guam last year was caused by part of the plane's tail assembly being set in the wrong position, a U.S. Air Force investigation report released Friday said.

The plane's stabilizer trim was improperly set between 4.5 and 5.0 degrees nose-down at impact, indicating the aircraft had been in a nose-down descent at low altitude, according to a report by the Air Combat Command in Langley, Va. The stabilizer trim is used in conjunction with the aircraft's elevator to control the pitch of the aircraft.

The unarmed bomber was on a training mission that included a flyby in support of the Guam Liberation Day celebration when it crashed in July off Guam, a U.S. territory located 3,700 miles southwest of Hawaii. All six crew members on board were killed.

The report said the reason why the stabilizer trim was improperly set could not be determined because there were no survivors or emergency radio calls from the plane. Only a minimal amount of aircraft control systems or instruments were recovered.

The investigation also determined that the combination of a low altitude and a descending left turn, and the crew recognizing too late the severity of the situation, contributed to the crash.

But the board said any experienced crew could have found it difficult to recognize, assess and recover from the rapidly developing situation involving the stabilizer trim setting.

The B-52 was assigned to the 20th Bomb Squadron at Barksdale Air Force Base in Louisiana.
Author:  Louis Emond [ Mon Feb 16, 2009 7:41 am ]
Post subject:  Trim Runaway
Some years ago the CAF lost a C-130 Hercules to what was found to be Vertical Trim runaway, a condition resulting from the trim system going to the end of trim after activation, I wonder if the B-52 system could be subject to this as well?
Author:  gary1954 [ Mon Feb 16, 2009 7:54 am ]
Post subject:  Re: Trim Runaway
Louis Emond wrote:
Some years ago the CAF lost a C-130 Hercules to what was found to be Vertical Trim runaway, a condition resulting from the trim system going to the end of trim after activation, I wonder if the B-52 system could be subject to this as well?


that is a very good question
Author:  Randy Haskin [ Mon Feb 16, 2009 9:03 am ]
Post subject:  Re: Trim Runaway
Louis Emond wrote:
Some years ago the CAF lost a C-130 Hercules to what was found to be Vertical Trim runaway, a condition resulting from the trim system going to the end of trim after activation, I wonder if the B-52 system could be subject to this as well?


Yes. The accident report (http://www.stripes.com/09/feb09/crash_report.pdf) gives two scenarios -- one is the "mis-set trim" as described in the first post. The second is "runaway trim".
Author:  b29flteng [ Mon Feb 16, 2009 9:30 am ]
Post subject: 
As an FE on C130s we practiced the runaway trim senerio in the sim. My job was to pull the circuit breakers for the trim to stop it. We had to memorize where these breakers were.
Author:  Dave Hadfield [ Mon Feb 16, 2009 11:02 am ]
Post subject: 
A "Runaway Trim" scenario has been a standard jet-abnormal drill since the early 1960s.

You've got to be fast with it. If it's the high-speed trim motor that won't shut off, and you're only a few thousand feet up....

Boeing configured the 727 to have a very large disc as a trim wheel, one of the reasons being that if a runaway occured, it was extremely obvious. With the DC-9, it was only a "tone". In the Sim it always took longer to recognize the fault in the DC-9 than the 727, with a consequent greater altitude divergence.

Dave
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