Aircraft Accident Report from the National Transportation Safety Board (NTSB)
- Data Report
Aircraft Involve: Havilland DHC-3T (Otter)
Flight Type: Charter/Taxi (Non-Scheduled Revenue Flight)
Date & Time: Jun 25, 2015, at 1215 LT
Flight Crew: 1 Airline Transport Pilot
A de Havilland DHC-3T aircraft flew from a fishing resort to a distant fishing spot when it crashed into tundra-covered terrain shortly after takeoff from a lake. The aircraft started to ascend after takeoff before starting to drop. The floats struck the water, then the seaplane briefly became airborne before crashing. The pilot reported that, before departure, the front and center fuel tanks were full and that the aft fuel tank had residual fuel. Before takeoff, the pilot estimated the weight and balance of the aircraft.
Causes of the Accident
The aircraft’s maximum gross weight was exceeded by around 508.6 lbs, according to a weight and balance investigation that took into account the weight of the passengers, weighted baggage, and fuel load, and revealed that the center of gravity (CG) was 4.08 inches aft of the aft CG limit. The pilot flew the aircraft outside of its weight and CG restrictions, preventing it from reaching a normal airspeed and ultimately leading to an aerodynamic stall. This was due to the pilot’s failure to identify the actual preflight weight and CG of the aircraft.
- Importance of Weight & Balance in General Aviation Aircraft
- The Aircraft Exceeded the Total Takeoff Gross Weight
The pilot relied on his estimation of the total gross weight before departure without taking into account the total weight of all the passengers, added baggage, and other relevant data.
- Unbalanced CG
Since the takeoff gross weight was exceeded, the CG was 4.08 inches aft of the aft CG limit.
- Preflight Calculations
Weight and balance calculations are important to ensure that the aircraft could be operated over its certificated takeoff gross weight or outside CG limitations. Executing proper preflight calculations will ensure that the aircraft is within the allowed weight and CG constraints based on Aircraft Flight Manuals (AFM). The maximum weight and CG restrictions for takeoff and landing are described in detail in each AFM or Pilot’s Operating Handbook’s limitations section.
An aerodynamic stall and loss of aircraft control, usually during takeoff or landing, can result from an aircraft flying outside of the CG limitations, both of which can significantly impair an aircraft’s performance characteristics.
As part of the preflight preparation, the pilot should calculate the distances for takeoff and landing. The weight will drop and the CG will vary as a function of fuel consumption during flight.
- Atmospheric Conditions
Analyzing the atmospheric conditions such as the gust intensity, density altitude, and temperature is important to ensure that these factors don’t affect the CG limits. Even when an aircraft is at or below its maximum gross takeoff limit, atmospheric circumstances might impair it to the point where it is unable to maintain a climb.
- Aerodynamic Stall
As the CG moves forward, the wing must produce more lift, and hence the stalling airspeed increases (Daidzic, 2022). The aerodynamic stall is caused by the implications stated about going beyond the CG limits.
Daidzic, N. (2022, January 17). Aerodynamics: Nothing but A Number A Closer Look At Stall Speed. AOPA. Retrieved February 11, 2023, from https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjGx67vzIz9AhWOsFYBHZHbAH0QFnoECBgQAw&url=https%3A%2F%2Fwww.aopa.org%2Fnews-and-media%2Fall-news%2F2020%2Fmarch%2Fflight-training-magazine%2Faerodynamics-stall-speed%23
Minding Weight, Maintaining Balance. (2018, February). NTSB. https://www.mlit.go.jp/common/001231152.pdf