# NTSB SEA97IA051: Beech 1900D, N75ZV, Seattle, WA, January 21, 1997 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: January 21, 1997, 06:20 local (14:20 UTC) - Place: Seattle, WA - Coordinates: 47.439357, -122.279739 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=47.4394&lon=-122.2797&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 7 uninjured - Status: Completed, report June 26, 1997 - Report: Approved by Office Director - NTSB case key (mKey): 42517 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA97IA051 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/42517/pdf - Page: https://openairdocs.org/ntsb/SEA97IA051 ## Probable cause an axial shift of the aft flap track bearing's outer roller, resulting in erosion and failure of the flap track bracket/bearing assembly. A factor relating to the incident was: inadequate inspection of the flap roller bearing/bracket assemblies. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, approach - vfr pattern - final approach - flt control syst,wing flap control bearing - shifted (cause) - flight control,flap attachment - eroded (cause) - flight control,flap attachment - disconnected (cause) - maintenance,inspection - inadequate, company/operator management (contributing factor) ## Analysis While on final approach, the airplane commenced a rapid, uncommanded roll to the right when the 35-degree flap setting was selected. The flying pilot (1st officer) was able to counter the roll by applying almost full opposite aileron, during which time, he felt the aileron jam momentarily and then break free. The airplane landed without further incident. An examination revealed that the inboard, aft end of the right wing outboard flap was detached from the wing flap track. This resulted in flap asymmetry and mechanical interference with the aileron. The flap track roller bearing was seized and the flap mounting bracket was torn and separated from the bearing. The bearing outer roller was loose and could be shifted axially on the bearing outer ring. This allowed the outer roller flange to wear against and eventually tear through the flap mounting bracket. The operator was not using the most recent (revised) Beech 1900D maintenance manuals at the time of the incident and the airplane had not been subjected to a detailed inspection of the flap roller brackets, roller bearings, and attachment hardware as outlined in revised sections of the manual. ## Factual narrative On January 21, 1997, about 0620 Pacific standard time, N75ZV, a Beech 1900D, operated by Mesa Airlines, Inc., as United Express Flight 7830, had a flight control malfunction during approach to the Seattle-Tacoma International Airport in Seattle, Washington. The airplane received minor damage and landed safely. The captain, first officer, and five passengers were not injured. Visual meteorological conditions prevailed and an instrument flight rules flight plan had been filed. The flight departed from Walla Walla, Washington, and was destined for Seattle. The scheduled domestic commuter flight was conducted under 14 CFR 135. In an interview with the Safety Board (record of interview attached), the captain stated that he began the day of the incident in Walla Walla, Washington, by performing a preflight inspection "by the checklist." The inspection included operating the flaps and running up the engines. The captain stated that "everything worked normally" during the inspection and run-up. The flightcrew then boarded the passengers and departed uneventfully from Walla Walla. The captain stated that he and the first officer briefed the instrument landing system (ILS) approach to Seattle, but planned on getting a visual clearance to the runway. Dark night conditions prevailed. The airplane broke out of the clouds about 4,200 feet, and the flightcrew was cleared for a visual approach to runway 16R. The captain stated that the first officer then called for "flaps 17." No problems were noted during the flap extension. The flightcrew then requested and received permission to land on 16L. The airplane was slowed to 140 knots, and the flightcrew was cleared to land on runway 16L about 3-1/2 miles from the airport. After getting lined up with the runway, the first officer called for "flaps 35." The captain lowered the flaps. He immediately heard a "whump" and saw the first officer move the control yoke. The first officer told him that he had a problem moving the controls. The captain stated that he did not want to have a transfer of control at that moment, so he elected to have the first officer continue to fly the airplane. The captain placed his hands on the yoke in an attempt to feel the control forces. He stated that the "controls felt restrictive." He elected to continue the approach and land in order to avoid a go-around, and he called for an increase of the airplane's "V-ref" airspeed by 5 knots to compensate for a potential "split flap." The approach was continued to a safe landing. The captain stated that the first officer "had to use a little bit of right rudder" during the approach and landing, and the control yokes were "about 3/4 of the way over" to the left. The captain stated that he was "thankful we were wings level" at the time of the incident, and he estimated that the incident occurred as the airplane was flying between 500 and 700 feet above the ground. He stated that no altitude was lost, and that the cockpit resource management during the incident was "excellent." The captain stated that the flap control was not moved after the landing and during the taxi to the gate. After parking the airplane, he egressed and inspected the airplane. He noticed that the right wing flap sections were "split" into an asymmetry; the inboard flap was lower than the outboard flap. He also stated that the inboard portion of the right outboard flap "came loose and cocked the aileron." He also observed that the "upper surface of the right outboard flap was in contact with the lower surface of the right aileron, " and the aileron was "hard to move" by hand. According to the first officer, who was the flying pilot at the time of the occurrence, the incident occurred when the airplane was about 500 feet above the ground, 140 knots, wings level, the "landing assured," and the flaps in transit from 17 degrees to the next and final setting at 35 degrees. The first officer stated that "a couple of seconds" after the flaps were beginning to lower, the "airplane started to abruptly turn to the right...at least 15 to 20 degrees." The first officer stated that he immediately "countered to the left" by moving the control yoke, at which time he "felt a pop." He stated that he "popped through and broke something loose" and "both hands were on the yoke at the time I did it." He also stated that the force needed to counter the right roll surprised him, and he reacted quickly. He first thought it may have been wake turbulence. He stated that if the situation would have occurred with a pilot who had less physical strength and size than himself, the abrupt roll "would have been a shock." The first officer stated that he needed to keep in left control yoke in order to keep the wings level. He stated that the control yoke was at "almost full deflection" to the left, and it was pointing toward the "nine o'clock or ten o'clock" position. He also needed to put in "some rudder to compensate." He stated that the situation would have been much more hazardous if the abrupt roll and jamming would have occurred while the airplane was in a right bank. The first pilot was the captain and non-flying pilot of the incident flight. He was an airline transport pilot and had been flying for Mesa Airlines since June, 1994. The first pilot reported that he had about 3,100 hours of total flight time, including 2,850 hours in type. The second pilot was the first officer and flying pilot of the incident flight. He was also an airline transport pilot and had been flying for Mesa Airlines since July, 1996. He reported that he had about 1,800 total flight hours, including 330 hours in type. The aircraft, a Beech model 1900D, was manufactured in 1993. Two flap sections are mounted on each wing of the Beech 1900D and travel in unison via an electric motor. The outboard edge of the outboard flaps are located next to the inboard edge of the ailerons. The inboard flap sections are larger than the outboard flap sections and incorporate sealed roller bearings to facilitate their movement. The outboard flaps sections incorporate non-sealed roller bearings. According to the Raytheon Aircraft Company, an upgraded design for sealed roller bearings had been company-approved prior to the Seattle incident, but the vendor was unable to provide the bearings at the time of the design approval. The flap system design for the aircraft incorporates asymmetric limit switches which are supposed to stop the flap movement when such a condition first develops. Two linkages are mounted between the flap sections and are connected to a device which incorporates a roller cam. Should one flap section continue moving while the other does not, the relative motion between the flap sections -- and thus the linkages -- causes the roller cam to ride up onto the flap limit safety switch, thus deactivating electrical power to the flap motor. The device is designed to activate should one flap section move more than 3 to 6 degrees relative to the other section, assuming the flaps remain properly connected to their attach brackets. An examination of maintenance records (excerpts attached) revealed that the Seattle incident airplane had accumulated 10,642 cycles. It received a routine inspection five days prior to the incident. The routine inspection did not include specific instructions of a detailed inspection of the flaps. The airplane also received a "detailed inspection" on November 2, 1996; according to the inspection checklist, no discrepancies were found on the flap skin or structure and the inspection did not include specific instructions to inspect the flap bracket or roller bearings. It was also determined that the airline had not been utilizing the most recent Beech 1900D maintenance manuals at the time of the incident. Because Mesa Airlines did not immediately report the incident to the Safety Board, the flap was removed and r ## Aircraft - Registration: N75ZV (not matched to a registry record) - Reported make and model: Beech 1900D - Category: Airplane - Serial number: UE-75 - Airframe hours: 7027 - Engines: P&W PT6A-67D 1279 horsepower turbo prop - Damage: Minor damage - Flight: Part 135 - Operator: Mesa Airlines, doing business as United Express - Registered owner: Mesa Airlines, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, January 16, 1997 - Departed: ALW, WALLA WALLA, WA - Destination: SEA - Flight plan: IFR - Airport: SEA, Seattle-Tacoma Int'L, runway 16L, 11,410 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 28; commercial, airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 3,100 total, 2,850 in this make and model, 600 as pilot in command, 240 in the last 90 days, 80 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/dark - Wind: 170° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: 4,000 ft broken - Temperature: 45 °F, dew point 37 °F - Altimeter: 29.00 inHg - Observed at: SEA, 2 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19970121005569I](https://openairdocs.org/incident/19970121005569I), Jan 21, 1997: Beech 1900D, Seattle, WA, Minor damage. Narrative: aircraft was on a two mile final and cleared to land. Crew selected 35 degree flaps from 17 degree when aircraft began abrupt roll to the right… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.