Misapplied Sealant Likely Caused Grumman Plane’s Fatal Ottawa Engine Failure

Misapplied maintenance sealant most likely caused the complete engine failure that preceded a fatal Grumman American AA-5A crash in Ottawa, according to the Transportation Safety Board of Canada’s investigation released October 23, 2026. Investigators found sealant residue throughout the engine crankcase and identified several major failures and discrepancies during the engine examination.

The finding connects a maintenance-material application error with internal contamination and loss of propulsion. It also resolves a critical operational question: flight-data calculations showed that the four-seat aircraft could not have reached any runway from its position and altitude when the engine failed, even if the pilot had acted immediately.

A rapidly worsening mechanical emergency

The aircraft departed Gatineau/Ottawa Executive Airport at 5:34 p.m. on July 31, 2025, in clear conditions. At 5:48 p.m., while approximately 800 metres above a populated part of Ottawa, an engine covering opened. The safety board reported that pieces separated from the engine and oil sprayed across the windshield, significantly reducing forward visibility.

Pilot Stéphane Tessier initially reported an oil leak and continued toward Rockcliffe airport. Less than a minute later, he diverted to Ottawa International Airport and received clearance to descend toward Runway 14. The propeller subsequently stopped. The aircraft struck trees about 960 metres short of the runway; Tessier died, while the two passengers sustained minor injuries.

The board assessed it as “highly probable” that complete engine failure had already occurred around the time the covering opened about three minutes before the pilot told the control tower that the engine was about to fail. That timing changes how the final approach is understood. The aircraft was probably already operating as an unpowered glider while the cockpit indications, oil release and external breakup were still being interpreted.

Why the runway was beyond reach

A runway can be visible, selected and authorized without being physically reachable. Once a single-engine aircraft loses propulsion, its available options are bounded by altitude, distance, aerodynamic glide performance and the energy consumed by turns. Oil across the windshield added a serious human-factors burden by impairing forward visibility just as the pilot needed to assess the aircraft’s condition, navigate over a built-up area and manage the descent.

Flight-data analysis found no attempt to land anywhere other than Runway 14. Tessier continued manipulating the engine controls and reassured the passengers that the aircraft could reach the runway. The board’s calculation nevertheless placed every runway outside the aircraft’s attainable glide area from the point of failure. The shortfall of approximately 960 metres was therefore not merely the result of a late warning or delayed clearance; the available altitude and position did not provide enough reach once power was lost.

The analysis also limits retrospective claims that a different runway selection alone would have solved the emergency. Rockcliffe and Ottawa International were both considered during the flight, but the investigators found that no runway was reachable when complete power loss occurred. The immediate constraint was energy, not airport availability.

Sealant is a material and process-control issue

The safety board used “most likely” rather than presenting the maintenance finding as absolute certainty. Its conclusion rests on the sealant residue distributed through the crankcase, the major engine failures and discrepancies, and the history of earlier maintenance. The reported facts support a maintenance-related contamination pathway, although the available account does not assign every observed engine failure to a separately described step in the sequence.

For maintenance organizations, the broader issue is that consumable materials can become system-level hazards when selection, preparation or application departs from the required process. Sealant is not treated safely merely because it is an approved aviation material. Its suitability depends on where and how it is applied, along with adherence to the relevant maintenance instructions and accepted practices.

Canadian maintenance rules reflect that process emphasis. Transport Canada’s Standard 571 requires personnel performing maintenance to follow manufacturer recommendations or equivalent accepted practices. It also requires records describing the work, the applicable reference when another standard is used, the date and the person who performed it. Those requirements create traceability, but the physical quality of the completed application remains the essential safety barrier.

A separate 2021 Cessna 180K accident in Ohio illustrates the same general material-control risk through a different system. The U.S. National Transportation Safety Board found that loose sealant contamination in a wing fuel tank likely obstructed fuel flow and caused total power loss. In Ottawa, the residue was found throughout the engine crankcase and the Canadian board tied it to major internal failures. The cases are not evidence of a fleetwide trend, but both show how material intended for maintenance can become damaging contamination when it does not remain properly applied.

For the Ottawa flight, that maintenance lapse had no recoverable runway margin once the engine failed. The aircraft was over a populated area, its forward view was impaired by oil, and every runway lay beyond the glide capability calculated from the recorded position and altitude.

By Thomas Caldwell — AMI’s senior editor for mechanical and mobility engineering, covering vehicle electronics, systems integration, electrification, chassis systems, propulsion, and safety policy.