Incident Overview
On 16 January 2019, during the descent of a Bombardier DHC-8-402 (Q400) to Poznań Airport (EPPO), the flight crew observed a MASTER WARNING 'CHECK FIRE DETECT', a P/B 'ENGINE FIRE' indication, and the illuminated PULL FUEL/HYD OFF handle for engine 1. The crew immediately executed the memory items and the checklist for an in-flight engine failure, fire, and shutdown. They shut down engine 1 and discharged both fire extinguisher bottles. The fire warning lights then extinguished.
The crew declared a MAYDAY and informed Poznań Tower of the fire indication. They continued the approach and landed on the remaining engine at 08:28 local time. The landing was uneventful. During the landing roll, the red fire warning light for engine 1 illuminated again. After taxiing onto taxiway S, the captain, accompanied by airport fire services, visually inspected engine 1 and observed no signs of fire. The crew concluded that the fire indication was false.
Post-Flight Inspection
Under escort by firefighting vehicles, the aircraft taxied to gate 42, where passengers deplaned normally. A subsequent inspection by the maintenance organization found no evidence of fire on the engine or airframe. During a check of the aircraft’s fire detection system, a fault was discovered at connector 2600-J24 (see Figure 1 of the report). Measurement revealed that the insulation resistance of the connector was lower than required.
Analysis and Cause
According to an analysis provided by Bombardier, the short circuit in the connector was likely caused by moisture ingress. The connector is mounted vertically and lacks proper sealing, allowing moisture to enter. Bombardier also reported that seven similar connector-related occurrences had been recorded in the global Q400 fleet.
Preventive Actions
The operator, PLL LOT, registered the event in its SMS database and initiated a campaign to replace connectors 2600-J24/J28 in the fire detection system on all Q400 aircraft in its fleet. During replacement, the connectors will be sealed using heat-shrink tubing or tape, following the manufacturer’s recommendations. The replacement is to be performed progressively during scheduled maintenance. Additionally, the flight crew’s actions were reviewed at the Q400 fleet instructor board.
Commission Findings
No safety recommendations or comments were formulated by the investigation commission.