Birgenair Flight 301

Birgenair Flight 301 was a flight chartered by Turkish-managed Birgenair partner Alas Nacionales ("National Wings") from Puerto Plata in the Dominican Republic to Frankfurt, Germany via Gander, Canada and Berlin, Germany. On 6 February 1996, the Boeing 757-225 operating the route crashed shortly after take-off from Puerto Plata's Gregorio Luperón International Airport.

Passengers
The crew consisted of 11 Turks and 2 Dominicans. The passengers consisted mainly of Germans, along with a few Poles. Most passengers had booked Caribbean package holidays with Öger Tours; Birgenair held 10% of Öger Tours. In terms of passenger deaths, Flight 301 has the highest death toll of any aviation accident involving a Boeing 757.

Crash
During takeoff roll at 11:42 p.m, the captain found that his air speed indicator (ASI) was not working properly, but chose not to abort takeoff. The co-pilot's ASI was functional. While the plane was climbing through 4,700 feet (1,400 m), the captain's airspeed indicator read 350 knots. The autopilot, which was taking its air speed information from the same equipment that was providing faulty readings to the captain's ASI, increased the pitch-up attitude and reduced power to lower the plane's airspeed. The co-pilot's ASI read 200 knots and decreasing, yet the airplane started to give multiple contradictory warnings that it was flying too fast, including rudder ratio, Mach airspeed and overspeed lights and sounds.

The autopilot reached the limits of its programming and disengaged. After checking their circuit breakers for the source of the warnings, the crew then reduced thrust to lower the speed. This immediately triggered the 757's stick-shaker stall alert, warning the confused pilots that the aircraft was flying dangerously slow, seconds after it was warning them that the speed was too high. The co-pilot and relief pilot both seemed to recognize the approaching stall and tried to tell the captain, but did not intervene directly, possibly out of deference to the captain's age and experience. The captain then tried to recover from the stall by increasing the plane's thrust to full, but the plane was still in a nose up attitude, preventing the engines from receiving adequate airflow to match the increase in thrust. The left engine stalled and flamed out, which caused the right engine, still at full power, to throw the airplane into a spin. Moments later, the plane inverted. At 11:47 p.m., the Ground Proximity Warning System sounded an audio warning, and eight seconds later the plane crashed into the Atlantic Ocean. All 13 crew members and 176 passengers were killed.

Investigation and final report
The Dominican Republic government's Dirección General de Aeronáutica Civil (DGAC) investigated the accident and determined the following probable cause for the accident: "'The crew's failure to recognize the activation of the stick shaker as a warning of imminent entrance to the stall, and the failure of the crew to execute the procedures for recovery from the onset of loss of control.'"

Investigations later showed that the plane was actually travelling at 220 knots at the time. The investigation concluded that one of three pitot tubes, used to measure airspeed, was blocked.

No tubes were recovered so investigators were unable to determine for certain what caused the blockage. Investigators suspected that some kind of insect could have created a nest inside the pitot tube. The prime suspect is a species called the black and yellow mud dauber wasp, well-known by pilots flying in the Dominican Republic. The aircraft had not flown in 25 days during which time the pitot tubes were not covered, giving the wasps an opportunity to build nests in the tubes.



Aftermath
While the crash was attributed to the failure of the crew to execute the procedures for recovery, there were a number of incidental lessons learned.

The pilot's choice to go against protocol and execute takeoff despite his ASI clearly disagreeing with the co-pilot's ASI has resulted in protocols and training being further reinforced following this incident.

After the flight voice recorder revealed that the co-pilot and a third pilot on the flight deck had made relatively subtle suggestions to the pilot - once the stick-shaker warning commenced - that he must deal with the fact that the plane was still in a speed-draining nose-up attitude, protocols and training were reinforced to establish a greater willingness of junior flight-deck staff to be more forceful in similar situations. (In the Birgenair crash, it had even been revealed that the co-pilot chose not to use his own, active, stick to counter the pilot and try to bring the nose down.)

Later the same year (1996), Aeroperú Flight 603, also involving a 757, suffered from a similar but far more difficult situation (static ports blocked by tape, rendering all airspeed indicators and pressure altimeters unusable) and crashed in the ocean off Peru.

In 1996 Birgenair went bankrupt.

Details of the crash have been revealed in the report of the Dominican Republic government's Dirección General de Aeronáutica Civil report and the Mayday television episode "Mixed Signals (The Plane That Wouldn't Talk)".