Investigation Summary
The disaster began during the takeoff roll from Mexico City. A dragging brake on the left main landing gear caused the tire to overheat significantly. After the gear was retracted, the heat transferred to the tire's internal gas. Crucially, maintenance personnel in Mexico City had previously filled the tire with regular compressed air rather than the required inert nitrogen. At high temperatures, the oxygen in the compressed air reacted with the rubber of the tire in a process called auto-ignition or 'thermal explosion.' The resulting blast ruptured fuel and hydraulic lines in the wheel well, leading to an uncontrollable fire that eventually melted the aircraft's structure, causing it to break apart at 31,000 feet.
Final Conclusions
The investigation concluded that the primary cause was the improper use of compressed air instead of nitrogen to inflate the tires. This maintenance error created a volatile environment where a dragging brake could trigger a tire explosion. The subsequent fire destroyed vital flight systems and structural integrity, leading to the total loss of the aircraft and all souls on board.
Video Analysis
Mexicana de Aviación Flight 940 – The Worst Air Accident in Mexican History — A detailed reconstruction of the 1986 crash of a Boeing 727 in the Sierra Madre mountains, claiming 167 lives.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Main Landing Gear
The site of the initial brake drag and subsequent tire explosion.
Hydraulic Systems
Lines were severed by tire fragments, leading to a loss of flight control surfaces.
Tire Inflation System
Required the use of nitrogen to prevent internal combustion; maintenance used compressed air instead.
Interesting Facts
- 01It remains the deadliest aviation accident in Mexican history.
- 02The aircraft was named 'Veracruz'.
- 03The tire was mistakenly filled with compressed air instead of nitrogen.
- 04The explosion occurred only four minutes after takeoff.
- 05A dragging brake during the takeoff roll provided the initial heat source.
- 06The Boeing 727 was the largest operator of its type outside the US at the time.
Safety Actions & Advisories
Nitrogen Inflation Mandate
Reinforcement of international regulations requiring the use of nitrogen for commercial aircraft tire inflation to prevent auto-ignition.
Brake Maintenance Procedures
Revised maintenance protocols for checking brake drag and ensuring proper brake bleeding to prevent overheating.