|Title:||Elevator control problems, Boeing - Canada (de Havilland) DHC-8-102, March 12, 2000|
|Micro summary:||This DHC-8-102 experienced flight control difficulties.|
|Event Time:||2000-03-12 at 1854 EST|
|Publishing Agency:||National Transportation Safety Board (NTSB)|
|Site of event:||Baltimore, MD|
|Departure:||LaGuardia International Airport, New York, New York, USA|
|Destination:||Baltimore-Washington International Airport, Baltimore, Maryland, USA|
|Airplane Type(s):||Bombardier DHC-8-102|
|Operator(s):||US Airways Express|
|Type of flight:||Revenue|
NTSB short summary:
the missing elevator stop bumper that resulted in elevator over-travel and damage to the elevator. A factor in the incident was the abrupt release of the elevator control lock in windy conditions.
During the flight, the airplane required full nose-down trim and forward pressure on the yoke to maintain level flight. As a result, a logbook entry was made, and inspection of the airplane revealed damage due to contact between the elevator and rudder. Examination of the elevator gust lock mechanism revealed that only three of four elevator stop bumpers were installed. The upper right bumper was missing, but the mount bolt was still in place. The upper left bumper was cracked, chipped, crazed, and displayed a longitudinal crack that ran its entire length. FDR data showed that when the airplane taxied onto the departure runway for the previous flight, the gust lock was released, and rapid deflection of the elevator control surfaces and the control yoke was noted. At the point where the control yoke returned to its nominal position, the LH and RH elevator graph lines were approximately 4 degrees apart. These lines remained separated by approximately 4 degrees throughout the remainder of the flight. Examination of prior flights revealed the elevator control surface graph lines were superimposed in all modes of flight. Winds at the departure airport were from 300 degrees at 22 knots, gusting to 27 knots. A product safety representative for the airplane manufacturer 'guaranteed' the airplane would have been undamaged during the rapid elevator deflection, had the elevator stop bumpers been installed.
NTSB factual narrative text:
On March 12, 2000, at 1854 Eastern Standard Time, a Boeing/de Havilland DHC-8-102, N838EX, operated by Allegheny Airlines, Inc., revealed sheet metal damage to the elevator and rudder during an inspection by maintenance personnel at the Baltimore/Washington International Airport (BWI) Baltimore, Maryland. The certificated airline transport pilot captain and first officer, the cabin attendant, and 29 passengers were not injured during the flight. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the flight conducted under 14 CFR Part 121.
The maintenance personnel were troubleshooting a logbook entry by the flight crew of US Airways Express flight 3678 that departed LaGuardia Airport (LGA), New York, New York, at 1630, and arrived BWI, at 1803. According to the write-up in the maintenance log, during the flight from LGA to BWI, the captain required "...Elevator trim at max nose down in climb, cruise, [and] landing attitude."
Examination of the elevator revealed damage to the inboard trailing edge fairing, inboard lower fairing, and right elevator spring tab. The rudder revealed damage on the top right forward edge.
In a telephone interview, the chief pilot of Allegheny Airlines said the airplane had experienced three crew changes during the day, and that the flight from LGA to BWI was the first flight of the day for that crew.
In a telephone interview, the captain said the preflight at LGA was divided between the first officer and himself. He said he performed preflight duties in the cockpit while the first officer examined the exterior of the airplane.
The captain said the flight experienced delays waiting for a ground power unit for engine start and while taxiing to the active runway. He said, "...the winds were strong and gusts were a little over 30 knots." The captain said that taxi, takeoff, and initial climb were "normal".
The captain said the airplane required a "significant amount" of nose down trim after climbing above 2,000 feet and 140 knots. He said that after level off, the elevator was trimmed fully nose down and the yoke still required slight forward pressure to maintain straight and level flight.
The captain was asked to describe the procedure that was used for release of the elevator gust lock on the ground. He said:
"The first officer released the gust lock. Normally, the first officer would release the gust lock taking the runway, but because of the winds, I asked him to release the gust lock on the runway centerline. There was no banging on release. The controls pretty much stayed where they were; there was no full travel of the controls."
In a telephone interview, the first officer said his exterior check of the airplane during preflight revealed no anomalies, and his account of the flight was consistent with the captain's. When asked to review release of the gust lock, he said:
"I take hold of the yoke with my right hand, and release the gust lock with the left. I didn't feel anything different."
Both pilots described the exchange of the flight controls, the pressure required to maintain level flight, and the discussion about a possible return to LGA. Both pilots said they felt they were in no danger and that they had full control authority with the airplane, so they decided to continue to BWI.
Data from the Flight Data Recorder revealed the airplane taxied into position for departure from runway 04 at LGA. Graphed lines depicting left hand (LH) and right hand (RH) elevator surface positions were superimposed over each other during taxi. At the point where the airplane aligned with the runway heading, during an approximate one-second duration, a 50 degree deflection of the elevator control surfaces and the control yoke was noted.
At the point where the control yoke returned to its nominal position, the LH and RH elevator graph lines were approximately 4 degrees apart. These lines remained separated by approximately 4 degrees throughout the remainder of the flight.
Examination of previous flights revealed the elevator control surface graph lines were superimposed in all modes of flight.
Examination of the elevator trim graph line revealed that full nose down trim was programmed during an approximate 6 second duration after the airplane accelerated above 120 knots indicated airspeed (IAS).
Examination of previous flights revealed application of approximately neutral pitch trim through all flight modes.
After removal of an inspection panel, examination of the elevator gust lock mechanism revealed that only three of four elevator stop bumpers were installed. The upper right bumper was missing, but the mount bolt was still in place. The upper left bumper was cracked, chipped, crazed, and displayed a longitudinal crack that ran its entire length.
The chief inspector for Allegheny Airlines prepared an Incident Report regarding the damage to N838EX. In the summary section, he stated:
"Initial inspection revealed the upper right elevator stop bumper missing, which in turn caused the damage to the elevator and rudder. While inspecting the mechanism in the horizontal stabilizer, we engaged the gust lock for the elevators, and inspected for play in the gust lock bracket attach plates. No defects were noted."
In a telephone interview, a product safety representative from de Havilland was asked if the damage could have been prevented had the upper right hand bumper been in place. He said, "I guarantee it. You wouldn't see the damage at all."
As a result of the investigation, maintenance and operational procedures for Allegheny Airlines and the Dash 8 fleet were changed by direct input from parties to the investigation and recommendations from the FAA.
In an electronic mail message dated May 8, 2000, Allegheny's Chief Inspector stated:
"...We are 100% complete in the inspection of our fleet for serviceability of the elevator bumpers and associated gust lock bracket. This inspection was prompted by the events that occurred on aircraft N838EX on Mar 13, 2000.
"We had no findings that I am aware of with the bumpers, however, several gust lock plates were found loose and repaired as necessary. The [Allegheny] C check is being revised to clearly state to inspect and replace these items as necessary..."
The de Havilland Dash 8 Flight Manual was revised on September 1, 2000 for "Introduction of Control Lock release Caution statement." According to the manual, "To prevent unrestrained elevator travel with the aircraft headed downwind, hold the control wheel firmly prior to releasing the gust lock."
The winds at LaGuardia Airport, at 1551, were from 300 degrees at 22 knots, gusting to 27 knots.
|Learning Keywords:||Operations - Bang, pop, crack, sizzle!|
|Operations - Maintenance|
|Operations - Trim Misset|
|Operations - Upset - Uncommanded or excessive Pitch|
|Systems - Elevator, Stabilizer, Rudder, Ailerons|
|Systems - Flight Control System|
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