What happened
On 11 February 2017, a Cessna 402C, registration N603AB, was performing a commercial passenger flight from St Thomas to Virgin Gorda. The flight was part of a series of short-duration legs, and the weather at the destination was excellent with clear skies and light winds.
Upon landing on Runway 03, the pilot retracted the flaps before applying the brakes. While the right brake initially responded, the pilot noted the right brake was not performing as expected, and the left brake pedal subsequently "flopped to the payload." Unable to stop within the runway limits, the pilot attempted to steer the aircraft away from the sea, eventually striking signage and a low wall. The aircraft's nose gear collapsed and the right main gear was broken off as it came to rest on a bank. There were no injuries among the nine occupants, though the aircraft sustained extensive structural damage.
The investigation
The AAIB examined the aircraft's braking system and maintenance history. Investigation of the brake master cylinders revealed significant issues. Both cylinders contained environmental dirt and aluminium flakes. In the left master cylinder, the filler plug was missing, and the internal reservoir was missing a rubber ring seal. Furthermore, fragments of a broken return spring were found inside the housing.
Testing also revealed that components from different manufacturers had been improperly interchanged between the left and right cylinders. The investigation noted that the aircraft had been involved in a similar braking incident at the same airport in 2008. Additionally, the investigators found that the performance data available to the pilot was invalid, as it did not account for the specific STOL modifications or the gravel surface of the runway.
Findings
- The aircraft landed in conditions where the required stopping distance was very close to the available runway length, leaving no safety margin.
- Debris and contamination within the braking system likely compromised braking performance.
- Maintenance shortfalls were evident, including missing seals, improper component installation, and the lack of available maintenance records for recent overhauls.
- The pilot lacked valid performance charts for the specific aircraft configuration and the gravel runway surface.
- The retraction of flaps after touchdown, a common company practice, further compromised landing performance.