There are a lot of aviation videos circulating on the internet these days. Some of them funny, some of them dramatic and some of them just have to be seen to be believed. One that always sits at the fore of my mind does so because it is absolutely chilling and the story behind it is equally sobering. Please watch this and then read on....
These were the final moments of an L19 Bird Dog and its occupants, captured by the ill-fated passenger. The aircraft, a single-engined Cessna was being used by the Forestry Department and lay undisturbed for a number of years following the crash, at which time the occupants and this footage were found. The family withheld the release of the footage for two decades before they generously allowed it to be shown so that others may learn. And yes, there is much to learn.
Firstly, the aircraft was operating on a summer's day in Colorado where the hills are high and the air is thin. Consequently, the ability of the aircraft to climb at this 'density altitude' is degraded in comparison to if it was flying along the coast on a cool day. The efficiency of both the wing to produce lift and the engine to produce power is reduced when it is hot, high and humid. A potentially lethal combination in the wrong circumstances.
Secondly, as the video evolves, the subtle killer of rising terrain begins to loom ominously. Towering mountains are easily spotted, but the approaching ridges of gently rising slopes is far less dramatic. At first, there seems to be little issue, but slowly and surely terrain is climbing towards the Cessna L19 at a greater rate than its performance can cope with. Ultimately the pilot realises that he can no longer out climb the ground below and the situation deteriorates rapidly.
The wing of the aircraft is now at such an angle to the passing airflow that the air is finding it difficult to continue to flow smoothly over the upper surface. This smooth flowing of the air is critical in the production of lift and the ability of an aircraft to fly. If you can imagine placing a paddle 'edge on' into a flowing river; the water flows past with minimal disturbance. If that paddle is then rotated with its flat face to the water-flow, the water no longer passes easily and disturbed 'eddies' bubble in its wake. In very simple terms, the air over a wing can behave similarly if it is inclined at too great an angle to the passing air. This is known as the stall.
Contrary to the average media reporting of an aircraft accident, 'stalling' has nothing to do with the engine spluttering. It is all about the wing's ability to produce 'lift' and keep it airborne. If the airflow cannot pass by easily and breaks into 'eddies' behind the wing, it can reach a point where it stalls. Lift is lost and the wing ceases to fly. The condition can be worsened by other contributing factors that we can discuss another time, but in this video, the pilot endeavours to turn the aircraft away from the hills and this actually accelerates the onset of the stall. The warning horn can be heard 'beeping' in the background advising the pilot of the impending stall and loss of lift. Sickeningly the aircraft begins to 'porpoise' as its nose goes up and down on the threshold of the stall until the combination of factors leads to one fatal flick and spin into the tree-line and the hopeless call of the pilot to his passenger of, ・Damn! Hang on Ronnie!・
Stall training and recovery is part of the training syllabus for pilots. However, it is often a manoeuvre that is either only briefly taught and/or only flown in copybook scenarios. Training of fully developed spins beyond the stall has also gone by the wayside for many training institutions outside of the military. As a consequence, stalling an aeroplane is touched upon in the early days of a student pilot and too often not revisited. As this video graphically demonstrates, the onset of a stall need not be a copybook or dramatic event, but a killer slowly creeping and lurking as it boxes the unknowing pilot into a corner.
This blog is only a thumbnail sketch of a very substantial and fundamental aspect of aerodynamics. Yet this video serves to demonstrate the potentially insidious nature of the stall. The families of the victims should be thanked for allowing this footage to be shared, for it truly is a graphic training aid for the instructors amongst us. That being said, flight is not inherently dangerous, but it can be brutally unforgiving. It is not the place of mere mortals like me to judge any aspect of this tragedy, but I hope that I have learned something of value. Otherwise, there but for the grace of God go I.
Please watch this one more time........
