Flying the Comet 4
Characteristics and Records


Peter Buggé described the Mk.4 as, “A pilot’s aeroplane” and this was the reaction of nearly all those that flew the Comet. The general feeling too was that the balance, aesthetically, was right – the aeroplane had grace and in the type 4 it was beautifully proportioned. There was some dispute as to which Comet was the most graceful – most people would choose the 4B as their personal choice.
The Mk.4 was in every conceivable way a better aeroplane than its predecessor. The new design was a model of efficiency and simplicity which extended to its operational characteristics – it was said to be a very easy aeroplane to fly. In service the Comet proved to be a remarkably tough and forgiving aeroplane.

New equipment on the Mk.4 included the Smiths Flight System, cloud-and-collision warning radar, V.O.R. and new power loss indicators which only required monitoring during takeoff.
To reduce noise a rolling start could be used – full throttle was selected and, with a quick check on the instruments and a report that fuel flow was OK. takeoff commenced with the Avons at 8000 rpm. The first officer monitored the engine instruments during the takeoff.
Ten knots before unstick speed the nose-wheel was raised – this was held until unstick speed plus 15 knts (V2 + 15) came up and, still on full power, at the about the 1200ft (20 seconds) point ,pulling back on the stick the Comet was airborne and making its characteristic steep climb.
The Comets power to weight ratio was exceptionally good and, should an engine be lost on takeoff, it did not have the slightest effect on handling. Even with two engines out on the same side, when the remaining two were at full power, the minimum control speed was close to the stalling speed (94 Knots at 110,000lb approach configuration). It was said that the most difficult thing about an engine failure was to discover that the engine had in fact failed!

At approximately 1200ft the throttles were pulled back to climbing power settings, around 7350 rpm. Once cockpit checks were completed the autopilot was engaged.
There were a number of techniques for the cruise-climb. In practice a fixed indicated air speed (I.A.S.). climb at 260 Knts was usually made (rather than gradually reducing I.A.S. with altitude) with marginal effects on economy and more significant effects in terms of ease and smoothness. The speed-lock on the autopilot was engaged when the correct I.A.S. is attained.
The crew could then take a breather until Mach 0.74 was indicated when the aircraft was trimmed to maintain the correct I.A.S. When the cruise altitude was reached the power was adjusted to take account of the outside air temperature.

Cruise Climb

Now the pilot had to opt either for a cruise climb or a fixed altitude cruise. In the former the aeroplane drifts up as it’s weight decreases and the I.A.S. had to be adjusted to maintain a constant Mach-number by approximately 2 knots every 20 minutes. This was a very economical method of operating but usually it did not suite the Air Traffic Control operators who generally preferred aircraft to maintain a constant altitude. When the fixed altitude cruise was the choice the height-lock on the autopilot was engaged and the I.A.S. and Mach number had to be adjusted from time to time.
In practice the differences in economy between these techniques was not great. The speed-lock held the I.A.S. within 2 knots of selection. Changes in ambient air temperature could result in a slow climb or descent and the Mach number varied too.

With height-lock engaged speed varied within wider limits. At 0.765M. an audible warning alerted the pilot to the excessive Mach number – if he fails to respond at 0.775 a recovery device would operate applying a small amount of up-elevator. Generally though it would take 0.8 Mach before a gentle nose-down attitude was induced in the Mk.4 and at 0.84 plus buffet was apparent. Turns might induce this at lower speeds but unlike some aircraft there was no wing drop. In excessive turbulence Mach number buffet might be induced at normal cruising speeds.


Stall characteristics

What about stalls? The wing design provided a number of small spoilers and fences on the leading edge. Essentially though in defining the Comet’s stall characteristics a compromise was necessary to provide safety margins in free air and ground conditions.

The ground stall was considered to be the more important and so the maximum angle could be attained at maximum take-off weight without problems. In the free-air state the compromise resulted in a degree of buffet if the stall was held. Since there was no natural warning of the approach of a stall a warning system was installed. A stick-shaker and warning red light was activated at 12% above stall speed.

In excessive turbulence the autopilot would disengage – but the outstanding handling of the Comet meant that there were no great problems piloting the aircraft through such conditions. And there was the benefit of ‘Q feel’. The rudder movement is limited too to 4° at over 170 Knots. In this way the pilot was better able to sense stresses and loading on the airframe and, hopefully, could avoid adding to them unwittingly by inappropriate manoeuvers.


Descent was begun some 200 miles from the destination. Now the inboard engines were brought back to ground idle rpm. – the spill-valves shed compressor-air with a characteristic roar. The outers were pulled back to give a steady 220 Knots – fine adjustment was made to regulate the cabin pressure.

Weather conditions could dictate the method of final approach. If suspect, the holding altitude (20,000 to 25,000ft) was maintained for as long as possible and then with the use of air-brakes a rapid descent (Max. 7000ft/min.) was made to the airfield.

The average rate of descent was approx. 1200ft/minute. Air-brakes, which produce only a little buffet and a slight nose-up attitude. (The use of air-brakes had an economic penalty and were not normally used). Whichever method of descent was used, cabin pressure had to be carefully regulated to ensure passenger comfort.


One peculiar effect of the very low external temperatures experienced in flight was that it cooled the metal structure within the cockpit and, as the descent continued, the high humidity of the cockpit resulted in condensation forming on the exposed metal. This happened particularly around the windows. It was said some crews got a regular soaking!

The autopilot could still be used on approach. On selecting 20° flap it brought in wider limit settings – so enabling coarser gear to be used. On approach, information from the I.L.S. was fed into the autopilot which allowed a ‘hands off’ approach to be made. If the approach was manual the Smith Flight System took the effort out of it.

The flaps were lowered in stages with full flap going down just before touch-down – effectively producing drag not lift at this stage. Full flaps could not however be applied at too great an approach speed because that produced excessive buffeting.

Just before touch-down the intent lever for the thrust-reverse mechanism was pulled back. As soon as all the wheels were down the reversers were operated (lifting the two outboard throttles would obtain reverse idle and pulling the throttles back gave full reverse power).

At normal landing weights without brakes the aircraft would stop in 1600 yds. With the Dunlop Maxaret anti-lock brakes the aircraft could be stopped in an emergency in 800 yds.

Truly a pilot’s aeroplane.



The Comet was not perfect though. On proving flights a number of minor problems came to light – nothing though that could not be rectified. Generally it was agreed that the air-conditioning was good but initially cabin temperature and air distribution was not sufficiently even. Inlet grills, near the floor for example, would be blow cold while the recirculation vents near the ceiling were warm. The public-address system needed balancing. The inboard engine blow-off valves caused noise and vibration making their presence felt to passengers. Operators complained that the size of the passenger doors could have been larger but more importantly the size of the freight door caused particular problems when rapid loading needed to be effected

As hours built up the Avons were granted extensions in their over-haul life. In the early 60s this had been extended to 2300 hours and the rate of unscheduled engine changes averaged less than 0.4% / 1000 engine hours – and the greatest proportion of these changes were due to bird ingestion!

Endurance Record

In July 1960 the Duke of Edinburgh flew to New York in a specially arranged BOAC flight to open the British Exhibition. The tour was routed via Ottawa and on the outward leg the Comet was in the air for 8 hrs 45 min. Commanded by Capt. Kelly (BOAC deputy flight manager), the aircraft arrived over-head at Ottawa with 5000 Kg of fuel in the tanks – and there was 3700Kg unused when the engines were stopped! Total distance covered was 3150 n.m. because the aircraft flew in a giant arc to take advantage of tail winds. On cruise-climb the Comet reached an altitude of 43,000ft where the outside temperature was -45 to -49°C.