Pilot Debrief

SHORT BROS SD3 60 SHERPA near Missoula, MT — 2016-10-13

Final reportWPR17IA007
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Date
2016-10-13
Location
Missoula, MT, USA
Airport
MSO
Aircraft
SHORT BROS SD3 60 SHERPA
Registration
N148Z
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Landing

Probable cause

The failure of the nose landing gear down-lock piston to engage due to paint accumulation, which resulted in a nose landing gear collapse during landing. Also causal was the failure of the facility that performed the painting to comply with manufacturer guidance regarding painting of the airplane.

NTSB narrative

The airline transport pilots reported that, during a ferry flight of an airplane that had just had been repainted, while on approach at its destination, the nose gear extended but failed to lock and subsequently collapsed on landing. Postaccident examination of the nose gear confirmed the nose gear's failure to lock, which led to its collapse. Observation of the nose gear down-lock actuator piston revealed that it had been painted, which prevented the piston from engaging and locking the nose gear during extension. Before the flight, maintenance personnel and the flight crew did not observe that the nose gear down-lock actuator piston area was painted. The airplane manufacturer issued a Service Information Letter (SIL) in 2007, that described a similar incident where the nose gear failed to lock in the down position on the first flight after an airplane had been repainted. The subsequent investigation revealed paint spray on the exposed piston of the nose landing gear down-lock actuator. The SIL stated "ensure that all masking material has been removed from the exposed piston after cleaning/painting, and that the piston is free from any paint or cleaning materials." Additionally, the landing gear emergency accumulator was observed during the preflight checks to be below the specified pressure. The accumulator was serviced to an adequate pressure prior to takeoff. Subsequently, the pressure bled down during the incident flight, and when the emergency landing gear extension was used by the flight crew, the accumulator did not have adequate pressure. According to the airplane manufacturer, the emergency landing gear extension is reliant on the main system pressure being depleted so that the emergency pressure can change a control valve position. Since the airplane's main hydraulic system was operative during the flight, the inability to use the landing gear emergency extension system, because of the lack of adequate pressure, would have been inconsequential, since the main system pressure was not depleted.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilots could have aborted landing after unsafe nose gear indication.

NTSB coding

  • Sys/Comp malf/fail (non-power) · Approach
  • Maintenance

Evidence available

  • Photos
  • 5 docket documents
View NTSB final reportView NTSB docket

Docket documents5

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