Yesterday we spoke of a possible scenario which resulted in the crash of a light aircraft shortly after leaving Essendon airport (YMES).
The original theory
When going through the checklist for a single engine failure, the pilot must ‘feather’ the engine/propeller of the failed engine, retract the undercarriage, and put the nose down for more level flight.
To “feather” a propeller means that the blades are turned such that their mid-to-outer section is aligned with airflow and they create minimal air resistance. This is done when the engine is shut down (or fails) so the propeller will create minimal drag.
A feathered propeller, minimising its profile to airflow
The landing gear is retracted also to minimise drag. These actions along with reducing the rate of climb, allow for the remaining engine to utilise maximum power to keep the aircraft in flight.
It is possible that none of this happened, it appears that either the pilot was not able to do this or he was prevented from running the engine failure checklist.
Industry experts believe the functionality of the plane’s auto-feathering feature, and how the engine was feathered, are the most crucial aspects of the crash.
It is possible the engine that failed did not auto-feather, or could not be feathered by the pilot. The result of the propeller not feathering correctly could have resulted in a windmilling propeller producing significant additional drag and have a deleterious effect on aircraft controllability.
A modified theory
There is a possibility of a second and possibly more immediate cause of the accident. However, before discussing this possible scenario, let’s have a quick look at take-off speeds in relation to engine failure.
V1 is the takeoff decision speed – if an engine failure occurs below this speed you abort or reject the takeoff (RTO). If engine failure occurs above this speed you must continue the takeoff.
Vr is the rotation speed – where the nose gear is raised off the runway surface but must allow the aircraft to accelerate to V2 before the aircraft reaches 35ft above the takeoff surface.
V2 is the takeoff safety speed – this minimum speed must be reached before the aircraft reaches 35ft above the takeoff surface with one engine inoperative.
Therefore if an engine failure occurs before V1, the takeoff roll is aborted.
If the engine failure occurred after V1 or Vr the takeoff was continued. However, if due to drag from a wind-milling (un-feathered) propeller, flaps extended and with the landing gear still extended, total power loss is not 50%, but can be as much as 80% even with the remaining engine operating at full power.
If the aircraft did not reach V2 it may not have enough airspeed to keep it airborne, eventually suffering a stall and crashing. The stall speed for a King Air B200 is 86 mph (75 knots, 139 km/h) IAS with flaps down.
In the video(s) of the incident, it appears that the landing gear was retracted, thus reducing drag.
ATSB investigations are continuing.
Words, By George! 