Boeing 727-200 Wing Strike During ILS Approach in Calgary

Incident Overview and Damage Assessment A regularly scheduled passenger flight operated by a Boeing 727-200 was delayed in Salt Lake City, Utah, due to poor weather in Calgary, Alberta. The delay extended the crew's scheduled duty day. Upon arrival in Calgary, the crew executed a flap-30, autopilot-coupled, instrument landing system (ILS) approach to runway 34 in low visibility. During the landing, the right wing struck the runway, causing damage to the wing tip, leading edge flaps, trailing edge flaps, flap screw-jack, and track fairings. The crew did not detect the contact until a post-flight inspection was completed on the Calgary ramp. No injuries were reported. ## Crew Background and Duty Day The flight crew's operating base was Atlanta, Georgia. The captain and second officer commuted by air to their base, while the first officer drove from Macon, Georgia. The crew was scheduled for an 11-hour, 30-minute duty day ending in Calgary. They operated flights from Atlanta to Minneapolis, Minnesota, and then to Salt Lake City, where a 2-hour, 30-minute scheduled wait was planned. The flight to Calgary departed approximately 1 hour and 30 minutes late after weather improved. The actual duty day until the crew disembarked in Calgary was about 13 hours and 15 minutes, which was within the limits permitted by company procedures and the pilots' association agreement for irregular operations. ## Approach and Autopilot Performance The aircraft intercepted the ILS glide path at 6,000 feet above sea level and maintained a continuous descent. The approach was flown at 142 knots indicated airspeed. The aircraft remained stabilized on the glide path until approximately 350 feet above ground level, after which pitch oscillations occurred. The captain disconnected the autopilot when a nose-down pitch was sensed. Shortly after disconnection, the aircraft began drifting left of the runway centerline. The captain attempted to correct the drift using right bank, and the aircraft touched down during this banked turn. The initial touchdown occurred with a bank angle of about 9 degrees and a vertical acceleration of 1.35 g, followed by a second touchdown with a bank angle of about 12 degrees and a vertical acceleration of 1.54 g. ## Autopilot Design and Regulatory Context The aircraft was equipped with a Sperry SP-150 autopilot, which is designed to reduce sensitivity as the aircraft approaches the ground to prevent overcontrolling. The desensitization process was originally scheduled over 150 seconds after the radio altimeter sensed 1,500 feet above ground level. However, the design assumed a flap-40 approach, whereas the standard practice at the time was a flap-30 approach, resulting in higher approach speeds. Sperry issued a service bulletin to reduce the desensitization time to 105 seconds, but the occurrence aircraft had not been modified. The United States National Transportation Safety Board (NTSB) had previously issued recommendations regarding the SP-150 autopilot sensitivity following a 1998 accident at Chicago O'Hare International Airport.