What happened
On June 26, 2003, a Piper PA-31-350 Chieftain, registration PH-PTD, was conducting a navigation training flight at Groningen Airport Eelde. The aircraft was carrying an instructor and three student pilots, along with one passenger. Following a successful VFR navigation segment and a subsequent go-around on runway 05, the crew prepared for a landing without the use of flaps.
During the final approach, a passenger noted that the aircraft appeared to be flying low according to the PAPI lights, prompting the pilot to increase power. As the aircraft transitioned to the landing phase, the throttles were pulled to the closed position. However, the landing gear had not been extended. The aircraft subsequently performed a gear-up landing, striking the runway with its tail before the remainder of the fuselage made contact. While the impact caused smoke and significant damage to the underside of the fuselage and both propellers, no injuries were reported among the five occupants.
The investigation
The investigation focused on why the landing gear was not deployed and why the cockpit warning system failed to alert the crew. The Piper PA-31-350 Chieftain is equipped with a 'gear unsafe horn' designed to activate if the landing gear is not in the downlock position while engine manifold pressure is below 12 inches of mercury.
Investigators found that none of the occupants heard the warning horn. Further technical examination revealed that the horn only triggered when the throttles were pulled back with extreme force. The physical effort required to activate the alarm was so great that the entire control quadrant moved during the process. While the system had passed its most recent 500-hour inspection, investigators noted that the mounting bracket for the 'gear unsafe' switch may have been slightly bent, though this was not definitively proven.
Findings
- The primary cause of the accident was the failure to extend the landing gear.
- The 'gear unsafe' warning horn failed to provide an audible alert to the crew during the critical phase of the approach.
- The mechanical resistance required to trigger the warning horn prevented the crew from receiving timely notification of the gear status.
- It remains unclear whether the crew omitted the final landing checks or failed to execute them correctly.