What happened
On August 15, 2003, a Gulfstream IV, registration A6-HHH, operated by Dubai Air Wing, was performing a commercial flight from Zurich to Dubai. Shortly after takeoff from Zurich-Kloten, the crew activated the wing anti-ice system, which was followed by a loud noise in the left wing root area. The crew then observed the left fuel gauge dropping to zero and received an "R WING HOT" alert on the EICAS.
As the aircraft climbed, a mechanic on board reported a rising temperature on the cabin floor and a pungent odor near the left wing root. The crew subsequently donned oxygen masks as the smell became noticeable in the cockpit. The flight crew declared an emergency, requesting an immediate return to Zurich. During the descent, the aircraft encountered heavy turbulence and thunderstorms. Despite experiencing various system warnings, including autopilot and yaw damper fluctuations, the crew successfully landed the aircraft at Zurich. The landing was performed at an overweight condition of approximately 69,000 lbs.
The investigation
SUST examined the aircraft and identified that a Gamah-brand clamp (P/N CA-33025) used to secure the wing anti-ice duct had failed at the hinge. This failure allowed high-pressure bleed air to escape from the duct, which connects the left engine to the wing leading edge. The escaping hot air heated the cabin floor and created the pungent odor reported by the crew.
Technical analysis of the broken aluminum rivets revealed that the failure was primarily caused by intergranular corrosion. The investigation suggested that the rivets, likely made of AlMg5 alloy, may have developed a corrosion-sensitive microstructure due to exposure to high temperatures during operation. This made the rivets susceptible to attack by moisture, such as condensation, leading to the structural failure of the clamp.
Findings
- The primary cause of the incident was the breakage of a pipe clamp, which allowed hot bleed air to escape.
- The escaping air heated the passenger cabin floor, resulting in a pungent odor.
- The failure of the left fuel gauge was likely caused by the heat from the escaping air affecting the sensor.
- The "R WING HOT" warning occurred because the pressure drop in the left anti-ice duct affected the right side via the crossover manifold, causing the right-side valves to move to maximum position.
- The rivets failed due to intergranular corrosion, potentially exacerbated by high-temperature service conditions.