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Kathmandu Plane Crash: Investigating the ‘Wing Stall’ Theory
Context:
Recently, a Bombardier CRJ200 jet carrying 19 passengers and crew crashed shortly after takeoff at Tribhuvan International Airport in Kathmandu. Captain was the sole survivor of this tragic incident.
More on News:
- A five-member panel led by the former Director General of the Civil Aviation Authority of Nepal (CAAN) is investigating the incident.
- The aircraft was seen banking steeply to the right before crashing. This extreme right bank, possibly caused by a wing stall, placed the plane in an unusual attitude.
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Unusual Attitudes and Aircraft Stability
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Key Highlights:
- The plane was transporting technicians for repairs on another aircraft in Pokhara.
- Historical Context: Nepal has a history of aviation accidents, with 69 recorded accidents causing around 900 fatalities since 1946.
- According to The Pilot’s Manual: Instrument Flying by Aviation Supplies & Academics, Inc (ASA), unusual attitudes include: 1) Bank angles exceeding 30°, 2) Nose-high attitudes with decreasing airspeed, 3) Nose-low attitudes with increasing airspeed.
- Regulatory and Safety Issues: The European Union banned Nepalese aircraft from its airspace in 2013 due to inadequate safety regulations. The ICAO recommended splitting Nepal’s Civil Aviation Authority into separate regulatory and operational entities, a reform pending for over a decade.
The angle of Attack and Stalls:
- An aircraft’s wings are designed with a cambered shape: curved on top and flat on the bottom. Lift is generated through the pressure difference between the top and bottom surfaces of the wings.
- This lift is effective as long as angle of attack (AOA)—the angle between the wing and the oncoming airflow—remains below a critical threshold (14-15°). Exceeding AOA leads to a stall.
- This condition impairs lift generation, resulting in sluggish controls and a nose drop. The stall can deepen without swift recovery, potentially causing the aircraft to spin.
Wing Stalls and Recovery Techniques:
- Wing stalls can occur if one wing stalls before the other, causing the aircraft to roll and bank excessively.
- Recovery from a wing stall involves pushing the nose down, applying the rudder opposite to the dropped wing, and keeping the ailerons neutral.
- Those fin-like movable surfaces are located on the wing’s trailing edge and close to the wingtip. An aircraft is banked by moving the ailerons.
Similar Case Studies
- In a previous 2023 incident involving Yeti Airlines Flight 691, the aircraft’s propellers were feathered (set to produce no thrust) for about a minute before the crash. This led to a stall, resulting in a catastrophic outcome.
- In 1992, a Pakistan International Airlines Airbus A300 crashed into a hillside near Kathmandu, killing all 167 people on board.