What happened
On May 1, 2022, at 15:28 UTC, a Bombardier Q400, registration SP-EQC, was performing an approach to runway 29 at Warsaw Chopin Airport (EPWR). During the landing gear extension sequence, the crew observed that the left main gear indicator showed an unsafe (RED) status and that the left landing gear door was open. Additionally, the landing gear control lever was not illuminated.
The crew immediately aborted the approach and requested an ascent to 6,000ft to enter a holding pattern to troubleshoot the issue. Upon checking the alternate landing gear extension panel, the crew found three green lights, indicating the gear was locked. The flight attendants also performed a visual inspection from the windows, confirming that the left gear was extended and the door was open.
After performing the "Alternate LDG Gear extension" checklist, the indications remained unchanged. Due to an easterly wind, the pilots decided to land on runway 11. The captain briefed the cabin crew for an emergency landing. Although the crew notified air traffic control of the emergency and requested ground assistance, they did not use standard emergency telephony (such as PAN PAN or MAYDAY). The landing on runway 11 was completed without further incident.
The investigation
The PKBWL investigation focused on the discrepancy between the primary landing gear indicators and the alternate system indicators, as well as the physical state of the gear confirmed by the crew.
Findings
- The direct cause of the event was the malfunction of a proximity sensor on the left main landing gear, which triggered an error in the Proximity Sensor Electronics Unit (PSEU). This error resulted in the incorrect display of the left main gear status on the Landing Gear Control and Indication Panel (LGCIP).
- The primary cause may have been the contamination of the proximity sensor.
Safety action
Following the incident, several corrective measures were implemented by the operator:
- The sensor was adjusted and tested, and the aircraft was returned to service.
- The operator's Quick Reference Handbook (QRH) was updated to clarify that the illumination of a single green light on either the primary or alternate system is sufficient evidence that the gear is down and locked.
- The Aircraft Operations Manual (AOM) was updated with specific instructions regarding landing gear indicator malfunctions.
- The operator issued internal communications emphasizing that the standard emergency calls, PAN PAN or MAYDAY, should be used immediately when an emergency or urgency situation arises.