What happened
On 23 November 2007, an APEX DR400/140B, registration EI-SKL, was performing training circuits at Weston Airport, Co. Kildare. While the aircraft was in a climb at approximately 200 to 300 feet after departing Runway 25, it experienced a sudden loss of approximately 40% to 50% of engine power.
Upon recognizing the partial engine failure, the instructor declared an emergency. Despite the loss of thrust, the pilot determined it was safe to turn back to the reciprocal runway. The aircraft was successfully landed on the grass area to the left of Runway 07, eventually rolling to a nearby taxiway where the engine was shut down. There were no injuries to the two crew members on board, and the aircraft sustained no damage during the incident.
The investigation
The investigation focused on the mechanical cause of the power reduction. An examination of the Thielert TAE 125-01 engine revealed that a silicone hose connecting the turbocharger to the intercooler had slipped off the turbocharger outlet. Although a Wiggins clamp was still in place, it had failed to secure the hose, allowing ambient air to enter the intake instead of the necessary compressed air from the turbocharger. This caused a significant drop in manifold air pressure.
Investigators also reviewed recent maintenance history and manufacturer communications. The engine manufacturer had previously issued Service Bulletins regarding the prevention of hose slippage. Notably, a revised bulletin had instructed the use of a single clamp rather than the double-clamp configuration previously required. The investigation noted that the engine type was still in its development stages, and the frequent removal of components for maintenance could increase the risk of connection failures.
Findings
- The engine power reduction was caused by the failure of the air connection between the turbocharger and the intercooler.
- The silicone hose slipped from the turbocharger outlet, allowing uncompressed ambient air to enter the engine intake.
- The air connection from the turbocharger to the intercooler failed when the adjoining hose slipped off.
- Contaminants such as oil in the airflow may have contributed to the hose slipping over time.
Safety action
- It is recommended that the engine manufacturer re-examine the design of the turbocharger pipe and hose connection to improve its security.