The problem with the tailplane was compounded by the thin skins on the fuselage cone which resulted in high twisting or torsional deflections. It was the asymmetric nature of the vibration which brought the tailplane undone. Part of production test flying for each airframe was a dive to 206 knots, and when the indon defence forces nomads came up for flying, the rear bubble window gave us the first chance to look at the tailplane outside of formation flying. So .....during a production test flight down to the back of the aeroplane did I trot, full of optimism. It was not a pleasant sight - you'd swear it was a rag tailplane and the dope had died. Shortly afterward stiffeners were added which kept it in shape a little better at speed. But the buffet induced from the wing with some combinations of flap and power (and that includes ground running) were large given that the tailplane was in the perfect position to suffer it.