Tony Blackman - Test Pilot: My Extraordinary Life in Flight

The 748 was a very challenging aircraft for a test pilot to be able to achieve the desired performance and, by modern standards, it was a demanding aircraft. Geoff Howett, an ARB test pilot who did the original flying with Jimmy Harrison, remarked that it was really two very different aircraft depending on whether it was flying on one or two engines. I think the point he was making was that the difference in flying skill required between flying on one engine and on both engines was much greater on the 748 than on other similar twin-engined aircraft.

The flying controls on the aircraft were all aerodynamically balanced; the ailerons were pleasantly light but the elevators and rudder were heavier, though of course all the forces could be trimmed out in steady flight. The time when the pilot really had to be in charge of the aircraft was on the approach when significant elevator forces were required when operating the flaps and when changing the power settings. In fact it was changes of trim with power which was the most significant, so that for a good approach, particularly on instruments, it was advisable to fly a steady speed on the glide slope. Pilots learnt the optimum way to fly the approach and we didnt have any problems with the airline pilots we trained once they got used to the aircrafts characteristics.

Flying on one engine was a very different proposition. The certification rules in those days allowed a pedal force of 180lb to be applied when determining the minimum speed the aircraft could be flown steadily on one engine, VMCA. This force is right at the limit for most pilots and certainly cannot be held for long; in fact it was reduced to 150lb some years later but of course the change did not apply retrospectively. In airline operation, the pilot should never have had to fly the aircraft at this speed since the minimum speed permitted was V2 which was 1.1 times VMCA. Nevertheless the rudder force to maintain V2 was still high and the sooner one trimmed the rudder forces the better.

It also had to be remembered that when an engine failed it was vital for the propeller to feather immediately to reduce the drag and the 748 was like all other propjet aircraft in that on engine failure the propeller was designed to auto-feather. Unless the propeller feathered it was almost impossible to control the aircraft on one engine.

When we were training airline pilots we would not actually close an engine down on take-off since this would have created an emergency situation unnecessarily. We only stopped an engine when we were actually carrying out test work such as measuring performance or determining critical control speeds. Instead we would simulate engine failure by throttling the engine back to about forty torque on the power gauge; throttling right back would actually create an adverse drag situation with the propeller. It usually took several take-offs before we were satisfied that the pilot under training could be relied on to accelerate the aircraft on the ground from V1 to VR, rotate the aircraft, allow it to accelerate to V2 and then climb the aircraft up to 400ft. This part of the training schedule was the most demanding, not only for the trainee pilot but also for the instructor. There were no simulators for the aircraft and, in reality, in the case of the 748 even had there been one I dont believe it could have substituted for having a real failure.

These days, control forces are much lighter and very often on a twinengined aircraft there is an automatic system so that if an engine fails some rudder is immediately applied towards the live engine to help the pilot. It was the high rudder forces on the 748 which caused the problem for the pilots.

There was another complication on the aircraft which was that it was necessary to choose the optimum amount of take-off flap depending on the length of the take-off strip and we certificated the aircraft for three settings, 7/2, 15 and 22/2. The shorter the strip the more flap was needed but in order to meet the climb out performance should an engine fail the maximum take-off weight would have to be limited with the higher flap settings. For this reason it was always very important that the pilot or dispatcher knew the flap being used so that the maximum take-off weight could be determined.