What aircraft was involved and where did it happen?

The accident on 2009-12-20 involved a Mc Donnell Douglas MD83, at FR.

What was the probable cause of the accident?

The incident was caused by a data entry error where the zero fuel weight was entered into the performance management system in place of the gross weight, combined with a lack of crew cross-verification of the performance parameters.

Data Entry Error Leads to High-Altitude Near-Stall in MD83

A Blue Line McDonnell Douglas MD83 experienced an approach to stall during cruise due to an incorrect aircraft weight entry in the performance management system.

What happened

On December 20, 2009, a Blue Line McDonnell Douglas MD83, registration F-GMLU, was conducting a positioning flight from Paris Charles de Gaulle to Kuwait. While cruising in the Reims FIR, the crew requested a climb from FL 260 to FL 370. After receiving clearance, the crew consulted the Performance Management System (PMS) and determined they could maintain a climb Mach of 0.65.

As the aircraft climbed through FL 300, air traffic control requested a 20-degree left turn. During this maneuver, the aircraft's airspeed began to decay. Upon leveling off at FL 370, the aircraft's Mach number had dropped to 0.67, and the autothrottle mode transitioned to indicate that the required thrust to maintain the target speed exceeded available limits. The crew reported feeling buffeting and noted that the airspeed was approaching stall speeds. To recover, the pilot manually disconnected the autopilot and initiated a left turn descent to FL 330. As the aircraft descended, the airspeed increased, the buffeting ceased, and the crew eventually stabilized the flight at FL 350.

The investigation

The investigation focused on the discrepancy between the aircraft's actual weight and the data entered into the PMS. Investigators found that during flight preparation, the pilot flying (PF) mistakenly entered the Zero Fuel Weight (ZFW) instead of the Gross Weight (GWT). Although an error message "CHECK GWT" appeared on the CDU because the entered value was below the required threshold, the pilot re-entered a value that cleared the error without verifying the actual GWT. The pilot not flying (PNF) failed to cross-check the entered data.

Furthermore, the investigation examined the aircraft's aerodynamic characteristics at high altitude. It was noted that for the MD80 series, the primary indication of an approaching stall at high altitudes is aerodynamic buffeting rather than the stick shaker, which may trigger much later. The investigation also noted that the crew's perception of the aircraft's performance was skewed by the belief that the aircraft was lighter than its actual weight.

Findings

The primary cause of the incident was an incorrect weight entry in the PMS, where the ZFW was entered instead of the GWT.
The crew failed to perform a cross-check of the performance data during the pre-flight and departure preparation phases.
The actual weight of the aircraft was approximately 126,500 lbs, significantly higher than the incorrectly entered value.
High workload due to previous delays and ground snow removal contributed to the oversight.
The aircraft's performance limits were exceeded because the thrust required to maintain the target Mach at FL 370 was unavailable at the actual weight.