Papa-India
Sir: Many of your readers will have a personal interest in the safety of air
craft. The official report on the Papa India trident crash seems to have swallowed the BEA scenario for this crash, "hook, line and sinker" viz. heart attack — droop lever — stall. For this court, despite other contribut ing causes, the real cause was Captain Key's incapacity from heart attack. They did not ask themselves whether a man of Key's age and family responsibilities could ever be found without a heart attack after such a shocking termination to a flight! Did they examine the others for heart attack?
Now I believe that the role of the droop lever has been greatly exaggerated. I propose an alternative scenario: — stall — droop lever — heart attack. Since events happened so quickly, BEA would have great difficulty in proving that their order of events is more probable than mine! Their scenario is very convenient for them and the engine suppliers: it enables them to divert not only criticism but scrutiny wa from efficiency of plane
and engines (ii) their training procedures (iii) their organisation for communication (iv) their take-off programme.
There is evidence that Papa India was far slower than it should have been at that stage of take off, and that the angle of attack (ie, to the horizontal) was rising fast. These are the crucial facts and we must ask why in connection with both. Assuming no majo structural defect, low speed usually means low power or overloading. The Court ascribes the low speed almos
Key's i it entirely to ey s incapacity or neg gence. The (lc; not seem. to enquire about engine defects or about loading. Was there any defect in fuel supplylines or any blockage of the air intakes? Normal engine revolutions could be very misleading if the engines were acting as vacuum exhausters rather than as compressors! Air-speed indicators based on Pitot Tubes are also hopelessly unreliable as all who have tried to callibrate a Pitot Tube must know! Yet the Report speaks of a shortfall of a mere 15mph in speed as a possible cause. Was the load excessive or badly distributed? Has the rear-flaps failed to retract properly? Failing all this what else could have made the plane slow with normal engine power at that stage of take off?
A plane stalls in the normal meaning when the angle of attack exceeds a certain critical limit; but orthodox hydrodynamic theory does not explain exactly why. The angle was rising! Did that experienced old hand, Captain Key, reach out for the droop lever to lift the droops at the front, instinctively, ie, just like a drowning man clutching at a straw? Was it a last desperate attempt, by a man who had tried everything, to reduce the rising angle of attack? Lifting the front droops would certainly not slow the plane down; on the contrary it would cut the drag and speed the plane. Indeed Key may have hoped for this. BEA asserted that it was this lifting of the droops which caused the stall; and they have got away with it! The action of front droops is said to be to delay the stall to a higher angle of attack. They almost certainly do this by increasing the lift. Unhappily they do this at the front of the wing — just as rear-flaps make lift at the back of the wing. Let us hope the BEA experts do not really believe that the lift is a single vector acting through a centre of lift!
If my views on this are correct the most urgent thing BEA have to do is to review their take-off procedure schedule again most carefully. In particular, since the Trident is tail heavy, it seems extremely odd that the rear wing-flaps are lifted long before the front droops! Is this not just asking for rising angle which is the only known proximate cause of a normal stall? If not then we all deserve an explanation as to why not!
If this is correct, Key's last throw in lifting the droops was perfectly rational! When this last throw failed is it not equally rational to suggest that heart attack then set in as a result of fear and panic? Most drowning men in fact do have heart attacks.
But we must still ask why it was not
possible to correct the rising angle by normal elevator or flap action? Did it , develop so fast that counter action was not possible? The nasty thought comes to mind: does a tail-heavy plane like the Trident, have an angle of no return above which the angle of attack must rise remorselessly, despite all counter action, towards the stall angle? It is clear to all that an excessive angle will slowdown the plane. 'If it could be shown that in a tailheavy plane, a plane which is. slowing down tends to sag further at the tail and lift the nose, then the vicious .circle I have postulated — with deceleration and rising-angle feeding each
other would become a practical possibility with horrifying implications!
Fleet Street suppressed a letter on . these lines early in February. The Russian Concorde has now crashed in very similar circumstances i.e. a very 'steep angle, so I feel it is my duty now to try to get, my letter published in the interests of all air travellers. My notion of an angle of no return (which was not in the earlier letter) now seems to take on a form which is more solid than a mere ghost or hunch.
J. W. Owen Dolgoed, Bala, Merioneth.
Previous page
