What happened
On November 10, 2015, a Boeing 737-400 was performing a takeoff from Istanbul (IST). After the flight crew moved the thrust levers to the takeoff position, a "TAKEOFF CONFIGURATION" warning light illuminated in the cockpit. The monitoring pilot identified the malfunction and notified the flying pilot, who was the aircraft commander.
Following the operator's Standard Operating Procedures (SOPs), the commander decided to continue the takeoff rather than aborting. The commander instructed the crew to move the flap lever to the takeoff setting. According to Flight Data Recorder (FDR) data, the flaps reached the takeoff position (setting 5) at a speed of approximately 143 knots. The aircraft rotation began at 154 knots, and liftoff occurred at 165 knots.
The investigation
The investigation focused on the crew's adherence to checklists and the technical capabilities of the aircraft. The investigation established that the crew failed to file an Air Safety Report (ASR) following the flight, though the event was eventually recorded in the operator's safety database after the monitoring pilot reported it via telephone and in person.
Findings
- The primary cause of the incident was crew error driven by excessive haste and a desire to maintain the flight schedule, which led to the omission of essential items on the "BEFORE TAKEOFF" checklist.
- The checklist in question contained three critical items: Flight Controls, Flaps, and Transponder.
- A contributing factor was the lack of a Takeoff Configuration Test system on the Boeing 737-400, which would have allowed the crew to detect configuration errors prior to entering the runway.
Safety action
- The operator's Short Haul Safety Pilot was notified and instructed to discuss the incident during an Instructor College meeting.
- The incident was documented in Safety Bulletin No. 10/2015.
- The investigation identified a discrepancy between the operator's Operations Manual (OM B) and the Quick Reference Handbook (QRH); while the OM B included a flap check during the "Before Taxi" procedure, the QRH did not. The investigation requested the inclusion of a flap check in the QRH, though the B737 fleet management subsequently decided against changing the checklists.