Canberra : Trainer Marks T.4 & T.13

The Canberra presented a unique operating challenge to the RAF when it entered service. Fighter pilots did not have multi-engine training but had jet experience, whereas pilots from the bomber stream trained on multi-engine aircraft and did not have any jet experience! The Meteor T.7 was temporarily adopted as a trainer due to the similarity of configuration to the Canberra with widely spaced wing mounted engines. It was clear however, that the Canberra had unique flying characteristics and a dual trainer version was needed.

The trainer version dubbed the T MK 4 first flew on 12 June 1952 and entered service in August 1953. It was a “minimal change” derivative of the Canberra B.2 bomber; the most noticeable visual difference was the T 4 had a solid nose instead of the glass nose of the B.2. Two pilots on ejection seats sat in the front fuselage, which was designed so that the layout of the B Mk 2 was preserved. This resulted in rather cramped accommodations for both pilots! The left hand side was, essentially, a B.2 – the pupil having been moved a little to the left of the B.2 seating position. The instructor was given a sliding and swiveling ejection seat, on the right side of the aircraft. The navigator had to crawl past the instructor’s seat, which slid forward, to his seat in the back of the aircraft after getting in through the lift-up door on the starboard side. At least the navigator had to just sit tight, during night checks it was commonplace for multiple pupils to swap seats in a running change. The instructor, after locking his sliding seat, was swiveled back and forth on his seat while the pupils crawled over him to get to the left seat or crawled over him to get out of the aircraft! Throughout the sortie the pupil pilot was craning his neck to the right because the “direct vision” panel blocked the view forward for the pupil! Meanwhile the instructor was craning his neck to the left! This was true for the RAF trainer versions (and the IAF's T.13s which are described later in this section) but the IAF's T.4s were a little more comfortable due to the elimination of the pilot's ejection seats.

In the Indian T.4s the instructor's seat moved fully back so that the pupil pilot could comfortably enter and exit his (there are yet to be any women Canberra pilots in the IAF) seat. The navigator could also enter comfortably when the instructors seat was in the full back position, which was the default position when the instructor wasn't actually sitting in the seat. If the navigator wanted to exit or enter with the instructor in place, he had to slip between the instructor's and pupil's panels and that was a tight fit.

In the IAF T.4s the pupil had good visibility and was comfortable in every way. The instructor was cramped with poor visibility. The instructors had to operate the controls with the left hand and the throttle with the right hand. The flying instrumentation was on the pupils side alone, with the engine panel in front of the instructor. According to an experienced QFI (Qualified Flying Instructor), "The QFI is just incidental from the designer's point of view!"

On the plus side, the T.4 had better performance than the B.2, being much lighter. It retained the bomb bay of the B.2 but was not used for bombing training, so without bomb beams and associated equipment it weighed about 7000 lbs less than the B.2.

It is surprising that the IAF’s adopted the T.4 and did not ask for a trainer based on the B.6 / B(I)58/ PR.7. The T.4s had the older Avon RA 3 engine of 6500 lb which none of the other marks adopted by the IAF had. This meant that a separate logistic chain needed to be maintained for the small number of T.4 trainers. The RAF had a large number of B.2s which had a common engine/airframe with the T.4 and didn’t have this problem. Given the changes that the IAF asked for the other marks, it would not have been too difficult for English Electric to fit a T.4 front fuselage to a B(I)58/PR.7 fuselage. This would have resulted in a trainer that had common characteristics with the operational aircraft of the IAF.

It is quite surprising that the Indian Air Force’s T.4s did not have ejection seats for the pilots. After English Electric had gone through a great deal of trouble to put ejection seats in T.4s, the IAF seems to have gone to a great deal of trouble to take them out! If any mark of Canberra needed an ejection seat it would have to be the T.4 – it spent so much time at low level in the “circuit” teaching pilots, and so much of its time doing engine-out practice (which could result in an out-of-control situation).

Canberra T.4 preserved at AFS Bareilly  (Sanjay Simha / www.warbirds.in )
Canberra T.4 preserved at AFS Bareilly  (Sanjay Simha / www.warbirds.in )

The Canberra T.4 was used for initial qualification training, Instrument Rating Tests (IRTs) and various checks for trainee and operational pilots. A critical regime that the trainee needed to be properly trained in was “engine out” or “asymmetric” handling. The Canberra was designed in an era when engine-out flight characteristics were not as stringently specified as with modern aircraft. This resulted in single engine safety speed ( i.e. the speed at which the aircraft could be safely controlled with one engine out and one engine on full power) which was high by modern standards. For the B.2 and the T.4 there is a 45 knots gap between the single engine safety speed and the speed at which it the Canberra lifted off the ground. In contrast a Boeing 747 Jumbo Jet has a safety speed that is below its stall speed, which means it is fully controllable with 2 engines out on one side and full power on the engines on the opposite side (the worst situation) at any time that it is flying. Whereas for the Canberra after liftoff, if there were problems with one engine before the safety speed was reached, engine power on the good engine had to be reduced to keep the aircraft in control. All this was counter intuitive to Canberra novitiates, since the aircraft had lost half its power already, was close to the ground and needed to climb away. This situation usually called for ALL the power one could muster. Without a simulator to practice this regime safely in an earthbound building, the Canberra T.4 was the torture machine that the pilot learned how to save his and his QFI’s life in!

The problem was the Canberra T.4 had handling peculiarities of its own. The Avon 101 (RA 3) engines are susceptible to compressor stall and have long spool up times. A compressor stall on the Avon 101 engine would produce a great deal of asymmetric yaw which at low speeds could result in loss of control. While carrying out an overshoot or a roller this could result in running out of airspeed, control and ideas. The result of such a scenario was not pretty.

The other problem with the T.4 was that it could not faithfully replicate all the characteristics of the operational marks of the IAF Canberras. One instance of this was again in the infamous asymmetric handling phase. The technique taught in the trainer for handling engine failure on take off was to throttle the good engine to 7000 rpm (51% power) rather than use full power (7800 rpm). The trainer climbed quite well at 7000 rpm (remember the 7000 lb weight saving in the trainer) and everybody assumed that this is the correct procedure. For the operational Canberra marks, especially at high weights, this amount of power is not enough to maintain height. After getting the aircraft under control, power needs to be gradually opened, within the limits of control. This last bit could not be taught faithfully in the trainer.

The T.4 was very valuable in teaching single engine flying techniques in the Canberra. The Canberra was generally considered a docile and forgiving aircraft except when operating on single engine. The pupil pilot was introduced to these regimes by experienced QFIs so that they could handle single engine emergencies when operational.

The Canberra had only two flap positions - up or down. It could not maintain height with flaps down on a single engine. Lowering flaps caused a change of trim causing the nose to rise and the speed to drop. Pilots had to be careful to trim down as the flaps moved down. It was critical that the flaps not be lowered too early, as single engine go-arounds with flaps down were dangerous and, therefore, prohibited. For a large part of the Canberra's service the SOP was to lower flaps at 600 ft on a single engine approach. However the flaps were slow acting due to a restrictor valve in the flap hydraulic circuit, which was introduced to reduce the effect of uneven flap deployment. It took approximately 12 seconds for the flaps to act. Pilots doing a single engine approach would lower the flaps, and seeing no immediate effect, would tend to reduce power. Then the flaps would take effect, increasing the descent rate and decreasing the airspeed. The pilots would either risk undershooting or would increase power on the single engine - which could lead to loss of control. There were fatal accidents on this account. The handling in this critical regime had to be introduced and practiced in the T.4 with an instructor, who prevented the pupils from getting into too much trouble.

The original SOP was evolved by the British Royal Air Force at a time when runway were generally 4800 feet long. 6000 feet was considered a long runway. Over time, the standard runway became 9000 feet long and the optimum procedure could be changed. The current SOP calls for deploying flap much later than the 600 ft height taught earlier. The flaps were used as "airbrakes", and pilots were encouraged to throttle back first to descend rather than use flaps. A higher threshold speed of about 130 knots was maintained, but with the longer runways that was not a negative factor. Once the runway was sure to be made the flaps were lowered, slowing the aircraft down (hence the "airbrake" effect). Remember that the flaps took 12 seconds to move fully down. If the flaps were lowered at 200 feet, they would be fully down only on reaching the threshold. This technique had the effect of not letting the pilots get into the critical regime of flaps down slow flight with a single engine at high power.

The T.4s gave yeoman service despite their shortcomings and introduced all IAF Canberra pilots to the Canberra. They are still doing that today!

Canberra T.4 at Agra  (Wg Cdr Vineet Bhalla )
Canberra T.4 at Agra . The aircraft belongs to No.106 SR Squadron with the "LYNX" emblem painted on the nose.  (Wg Cdr Vineet Bhalla )

Introduction of the T.13s

The Royal New Zealand Air Force (RNZAF) had acquired Canberra B(I) 12s and Canberra T.13s in 1958. The B(I) 12s were based on the IAF’s B(I) 58s, with equipment fit very similar to the B(I) 58s. Two trainer aircraft, based on T.4s but with an autopilot and an additional bomb bay fuel tank installed were also supplied to the RNZAF. These trainers were designated T.13 which were delivered to the RNZAF in 1961.

The IAF bought 8 B(I) 12s (which will be covered in the B(I) 58 section) and 2 T.13s from the RNZAF in November 1970.

The T.13s differed from the IAF’s T.4s because they provided ejection seats for both the pilot in the left hand seat (the trainee) and the pilot in the right hand seat (the instructor). Recall that the IAF’s T.4s had no ejection seats for the pilots up front. The navigators had ejection seats in both the IAF’s T.4 and the T.13.

The B(I)12s were almost exclusively used by 35 Squadron till 1977, along with one T.13 Q1191. They were then distributed between 16 Squadron and finally 6 Squadron.

The T.13 Q1191 went to 106 SRS in 1978, when 35 Sqn converted to the EW role.

T.13 Q1192 was used by ASTE (Aircraft and Systems Testing Establishment) in its TPS (Test Pilots' School). Wg Cdr Joseph Thomas, the first Commanding Officer of the TPS (as Sqn Ldr in 1973), has this to share about Q1192. “Q1192 was with ASTE and I have a lot of hours on it. The outgoing Naval Chief (Chief of Naval Staff Admiral Arun Prakash – a qualified test pilot) has flown it. I don't know whether any other Indian naval pilot has flown Canberras.”

The author also has a personal connection with Q1192. In 1983 the author had the privilege of staying with the then Chief Test Pilot (CTP) of ASTE, (then) Gp Capt IS Sandhu. On a visit to ASTE, the author was lucky enough to converse for about 20 minutes with a TP trainee doing a cockpit evaluation on the Canberra trainer. The author had a marvelous time crawling around in the cockpit. Alas, there was no camera available. Otherwise there would have had some memorable photographs, if permission had been forthcoming!

The T.13s got phased out in 1989, along with a host of other Canberra following the fatal accident of B(I)66 IF-1020 at Pune. Wg Cdr Vineet Bhalla is still incensed about the way this phase out was done. Here is what he had to say “The reason was that the Court of Inquiry wrongly deduced Canberra structural failure of the fin, when in fact the fin was found intact in the debris. I burn even today when I think about the way the inquiry went. I was the specialist flying member.”

The table below gives some characteristics of the Canberra T.4/T.13

Canberra T 54 / T 4/T 13 characteristics
Engines Rolls Royce Avon Mk 101 (RA 3) rated at 6500 lbs (2948 kg) thrust
Accommodation Two pilots and one navigator in ejection seats
Ejection seats Martin Baker Mk 2 CA (navigator)
(Only on RAF T.4s - Martin Baker Mk 3 CT  for pilots) – none in IAF T.4s
Martin Baker 3CT for pilots in T.13
Total fuel capacity 1874 gallons/ 14650 lbs + extra tank in bomb bay (T.13 only)
Operational equipment VHF (ARI 5490)
ILS (ARI 18011) and Zero Reader
IFF Mk 10 (ARI 5848)
API (Air Position Indicator)
Autopilot (T.13)
Basic empty weight/ MTOW 22000/37000 lbs

 

Indian Air Force Canberra T 54 / T 4 serial numbers
Mark Particulars Year Nos Indian Serials
Canberra T.4 Initial order ex-RAF XK647 & XK650 1958 2 IQ994 & IQ995
Canberra T.4 Initial order new build 1958 4 IQ996 - IQ999
Canberra T.54  Initial order option taken 1959 1 IQ985
Canberra T.4  Refurbished T.4 WJ859 1963 1 BQ744
Canberra T.4  Refurbished T.4 WH847 1968 1 Q495
Canberra T.13 From RNZAF T.13 NZ6151 & NZ6152 1970 2 Q1191 & Q1192

Total : 11 (7 new T.4s, 2 refurbished T.4s and 2 T.13s). Two T.4s embargoed and never delivered Q496 (ex-WH845) and Q497(ex-WE191)