What happened
On September 22, 1994, a Boeing B-747-400 operated by Korean Air, registration HL-7479, attempted to depart Zurich Airport (LSZH) on a ferry flight to Pusan, South Korea. The aircraft had previously suffered significant hail damage during a flight from Rome to Zurich on September 14, affecting the cockpit windows, radome, wing leading edges, and engines. Although repaired sufficiently for flight, Boeing imposed strict operational limitations due to increased drag.
The captain decided to utilize Runway 14 instead of waiting for the closure of Runway 16 to end. Consequently, the aircraft taxied via taxiways N, E, and D and began its takeoff roll from an intersection rather than the runway threshold. The tower did not suggest using the full runway length, nor did the crew request it. The aircraft lifted off near the end of the available pavement and cleared nearby buildings by approximately 50 meters (164 feet). It landed safely in Pusan later that day.
The investigation
SUST examined the operational constraints imposed by Boeing for ferrying a hail-damaged aircraft. These restrictions included reducing maximum takeoff weight by 70,000 pounds and increasing rotation speeds (V1, VR, V2) by specific margins (15, 14, and 17 knots respectively). The investigation confirmed that the aircraft's actual takeoff mass was 775,000 pounds. Calculations showed this exceeded the limited weight allowance for a takeoff from intersection D by 86,700 pounds. Even if the full length of Runway 14 had been used, the aircraft would still have been overweight by nearly 16,000 pounds.
Furthermore, the crew failed to apply the mandated speed increases, raising speeds by only 2 to 4 knots instead of the required 14 to 17 knots. The captain later stated he ignored these restrictions because a previous report indicated the damaged aircraft performed normally, and he wished to avoid delaying the arrival in Pusan.
Findings
The incident was caused by the failure to comply with manufacturer-imposed ferry flight limitations for a hail-damaged aircraft. Specifically:
- The aircraft was significantly overloaded for the available runway length from the intersection used.
- Takeoff speeds were not increased as required by Boeing's performance data.
- The captain relied on anecdotal evidence of normal performance rather than specific ferry flight restrictions.
- Air traffic control did not intervene or suggest using the full runway, assuming the crew was aware of their operational status.
The aircraft's ability to clear obstacles was purely fortuitous; a single-engine failure during takeoff would likely have resulted in a crash.
Safety action
SUST recommended that authorities examine whether ferry flights requiring performance data outside standard flight manuals should require prior authorization. This incident highlighted the risks of deviating from manufacturer limitations based on pilot discretion rather than strict adherence to engineering constraints.