What happened
On February 2, 1995, a Boeing 737-2A1, registration PP-SMV, operated by VASP, departed São Paulo/Guarulhos International Airport (SBGR) bound for Buenos Aires, Argentina. During the initial climb, the crew noticed a persistent "leading edge transit" warning light. In an attempt to resolve the issue, the crew decided to recycle the flaps.
This action triggered a catastrophic sequence of events. The recycling process caused the failure of hydraulic system "A". Simultaneously, the pilot reported that the number 2 engine thrust lever became stuck, maintaining high power (EPR 2.11). Faced with these critical failures, the commander elected to return to SBGR for an emergency landing.
During the approach to runway 09L, the aircraft was unable to decelerate sufficiently. The aircraft touched down at approximately 185 knots and overran the runway limits. During the excursion, the aircraft drifted right and then swung left, causing the right landing gear to collapse. The number 2 engine was torn from its mount and dragged under the fuselage. During the emergency evacuation, one passenger sustained serious injuries, five others suffered minor injuries, and 112 passengers remained uninjured.
The investigation
CENIPA investigators focused on the leading edge flap number 3 actuator attachment. They discovered that the aluminum support bracket was susceptible to stress corrosion cracking. This structural failure caused the actuator to separate, which subsequently severed hydraulic lines for system "A", the standby system, and the return lines. This breakage also interfered with the control cables for the number 2 engine's thrust and fuel levers, causing the engine to remain at high power.
Regarding the hydraulic systems, the investigation found that the standby system failed due to an internal leak in a magnesium-piston hydraulic fuse, which had not been replaced with the recommended aluminum version. Furthermore, while the aircraft's weight was approximately 4,500 lbs above the maximum landing weight, the braking capability was severely compromised because the hydraulic accumulator for the internal brakes was also malfunctioning due to low pressure.
Findings
- Design deficiency: The aluminum leading edge flap support was prone to stress corrosion, and the aircraft's design allowed a single component failure to trigger a cascade of multiple critical system failures.
- Maintenance deficiencies: The operator had not replaced the magnesium-component hydraulic fuse as previously recommended by a Service Bulletin, and the internal brake accumulator was presenting pressure issues.
- Operational errors: The crew failed to use the checklist before recycling the flaps, leading to the hydraulic failure. Additionally, the crew forgot that the trailing edge flaps could be extended electrically during a hydraulic failure, which resulted in an approach speed approximately 32 knots higher than necessary.
- Crew Resource Management (CRM): The investigation noted high workload for the commander and a lack of effective communication and coordination between the crew members during the emergency.