A Swearing SA226-TC Metro II was operating a scheduled passenger flight on this day in aviation history. Onboard the aircraft was a crew of two and eight passengers for the flight from St. Therese Point Airport to Winnipeg-James Armstrong Richardson International Airport.
The jammed right-hand main landing gear (source TSB © Department of National Defence)
After an uneventful flight as the aircraft was approaching Winnipeg gusty weather;
Wind - 180º at 20 knots, gusting 30 knots
Visibility - 15 miles with drifting snow
Clouds - broken at 12.000 feet
Temperature - -9ºC
Dewpoint - -7ºC
Altimeter - 29.00 inHg
As the aircraft was being configured for the landing, the crew selected the landing gear down. A short while later the nose landing gear and left-hand main landing gear indicated down and locked. The right-hand main landing gear however remained "In Transit". The landing gear was cycled several times, with no change in the indication, the right-hand main landing gear remained "In Transit" and would not lock down. A missed approach was flown and ATC was informed about the situation, stating that they needed time to troubleshoot the defect and get in touch with the company's operations en maintenance departments.
The jam simulated after the aircraft was jacked up after the accident (Source & © TSB)
As per the emergency checklist an emergency gear extension was carried out, again with no success, the right-hand main landing gear did not go into the down and locked position. The gear was checked from the cabin and appeared to be hung up (jammed) in the wheel well with the gear bay doors partly open. After briefing the passengers about the situation, a touch-and-go was flown in an attempt to free the gear, but this was unsuccessful. With the fuel level reaching the legal minimum, it was decided to retract the landing gear and perform a gear-up landing. This landing was uneventful after the aircraft came to a stop the aircraft was shut down according to the relevant checklist. Passengers and crew evacuated the aircraft through the main cabin door, with the airport fire brigade standing by. There were no injuries.
The aircraft was lifted from the runway and the emergency gear handle was pulled. All three landing gears immediately free-fell from their respective wheel wells and the landing gear was hand-pumped to the down and locked position. The aircraft was towed to the operator’s maintenance facility for further examination.
The Transportation Safety Board of Canada (TSB) was alerted and an investigation was initiated. The damage to the aircraft was recorded as abrasion damage to the;
Main Landing Gear doors
Flaps
Aft belly
(a) Damage to the ledge area of the raised inner skin panel (b) Wear marks from contact with the aft nacelle channel stop (Source and © TSB)
Furthermore, it was discovered that the right inboard gear door had a pronounced bend on the outer skin panel and an indentation in the raised inner skin panel with rub marks from contact with the number three tire. It was found that the gear door actuating linkage for the right inboard gear door was about 1/8 to 3/16 inches shorter than the other three gear door link rods. Maintenance records revealed that the last maintenance action on the landing gear door was carried out on the 25th of September 2008 on a Phase 8 5 inspection, 513 flight hours or 663 cycles before the accident. The right main gear inboard door was removed for sheet metal repair. The gear door was repaired and reinstalled along with a new aft hinge.
The TSB concluded their report (which served as the source for this blog) with the following findings as to cause and contributing factors;
1. The right inboard landing gear door was incorrectly rigged, which reduced the clearance between the tire and gear door during gear extension. The mis-rigged landing gear door likely went unnoticed through four separate inspections.
2. The combined effect of the mis-rigged gear door, the installation of a new re-capped tire with large dimensions, growing free play in the gear door bushings/linkage arrangement, and air loading on the gear door reduced clearances sufficiently that the number three tire caught on a ledge on the inboard door skin, preventing the right main gear from extending.
Several safety actions were taken and more details on this accident can be found in the TSB report, which can be accessed by clicking on the .pdf file below;