Main Cargo Door Opens Inflight on Boeing 757 Freighter

Casualties unknown • nahe Leipzig, DE

A Boeing 757-236 PCF cargo aircraft experienced a major malfunction when its main cargo door opened during initial climb, forcing an emergency return to Leipzig/Halle.

What happened

On February 13, 2021, a Boeing 757-236 PCF freighter departed Leipzig/Halle Airport bound for Frankfurt am Main. During the initial climb phase, the aircraft's main cargo door unexpectedly opened. The crew immediately declared an emergency and initiated a return to the departure airport.

The aircraft's flight characteristics were significantly altered by the open door, making it impossible for the autopilot to maintain the required flight path for a standard turn back to the airport. The pilot had to take manual control to execute the return. Despite the high risks associated with the altered aerodynamics, the crew performed an automated landing. There were no injuries to the crew, though the aircraft sustained light damage.

The investigation

The BFU investigation focused on why the door was able to open and why the crew was not alerted to the improper latching. Investigators examined the hydraulic-mechanical sequencing of the door system, the status of the cockpit warning lights, and the physical condition of the locking mechanisms. The investigation also included tests regarding ice accumulation on microswitches and the structural integrity of the vent door linkage rods. Findings revealed that while the door appeared flush with the fuselage and the cockpit warning lights were extinguished, the door was actually closed but not fully locked or secured.

Findings

The primary cause of the incident was that the main cargo door was closed but not fully locked and secured, a condition that was not indicated on the cockpit control panel or visible from the exterior. Several contributing factors were identified:

  • Adverse environmental conditions involving low temperatures and freezing fog, which led to ice buildup on the microswich mechanisms.
  • Air trapped within the hydraulic system caused a hydraulic sequencing problem, which prevented the locking pins from properly engaging.
  • The locking rods for the vent doors were not sufficiently rigid, allowing the vent doors to close even though the main cargo door was unsecured.
  • Aerodynamic forces acting on the door during the climb were powerful enough to overcome the door's weight and hydraulic pressure, forcing it fully open.
  • A faulty rear microswitch in the locking pin system contributed to the failure of the crew to receive an accurate status indication.

Probable cause

The main cargo door was closed but not properly locked or secured, and this unsafe state was not detected by the crew due to a lack of cockpit warnings and the absence of visible external indicators. This was exacerbated by ice accumulation on the locking mechanisms and a hydraulic sequencing error.

Frequently asked questions

What happened in the 2021-02-13 Boeing Company 757-236 PCF accident near nahe Leipzig, DE?

A Boeing 757-236 PCF cargo aircraft experienced a major malfunction when its main cargo door opened during initial climb, forcing an emergency return to Leipzig/Halle.

What aircraft was involved and where did it happen?

The accident on 2021-02-13 involved a Boeing Company 757-236 PCF, at nahe Leipzig, DE.

What was the probable cause of the accident?

The main cargo door was closed but not properly locked or secured, and this unsafe state was not detected by the crew due to a lack of cockpit warnings and the absence of visible external indicators. This was exacerbated by ice accumulation on the locking mechanisms and a hydraulic sequencing error.

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