B-52 crash at Guam: report released
- From: "Paul Hirose" <jvcmz89uwf@xxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 1 Mar 2009 16:03:23 -0800
Air Combat Command has released their report on the B-52H crash last
July in the ocean 30 miles from Guam that killed all six aboard.
"The Accident Investigation Board President found by clear and
convincing evidence that the cause of the mishap was a mis-positioning
of the stabilizer trim mechanism."
Analysis of the recovered stabilizer jack screw pointed to an 4.5 to 5
degree nose down setting. There was insufficient evidence to determine
the reason for this condition (the wreckage is 12,000 feet down), but
according to the report, the most likely scenario was a runaway trim
malfunction during a descending turn.
This was supposed to be a local training mission, beginning with a
flyby of the Guam Liberation Day celebration at 1000 feet and 300
knots. After takeoff at 0859 local, the B-52 entered a holding pattern
30 miles from the island at 14,000 feet as briefed. The desired "time
over target" was 1000. At 0952 the crew told ATC they were one minute
from initiating descent. That was their last transmission.
Based on radar returns, at 0953:11 the plane was straight and level at
240 KCAS and 14,100 feet. About 65 seconds later, at the last
transponder reply, it was at 2300 feet, an estimated 33 degrees nose
down and 510 KCAS. Heading changed about 60 degrees to the left
initially, but was practically constant for the last 20 seconds. Only
about 5 miles were traveled over the ground, for an average descent
angle of 25 degrees.
The board came up with two scenarios to explain the abnormal nose down
trim. One was that the pilot simply overtrimmed when beginning the
descent, then failed to recognize and correct the condition in time.
This was thought possible but improbable due to the experience of the
crew and the amount of time they would have to delay before attempting
recovery.
In the opinion of the board president, the most likely scenario was a
stabilizer trim runaway when the pilot began trimming nose down in the
descending turn. If the trim system failed to stop, simulator runs
demonstrated that even an expert crew could easily get into an
unrecoverable dive.
http://www.acc.af.mil/aibreports/
The B-52 report is a PDF of about 12 MB. It's only 33 pages long; the
great size is because the document is an image of a hardcopy.
Last year was a bad one for bombers at Andersen AFB, with the
destruction of a B-52 and a B-2, and serious damage to a B-1 in a
ground accident.
--
Paul Hirose <jvcmz89uwf@xxxxxxxxxxxxxxxxxxxx>
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