By Air Mshl M S D Wollen (Retd)
The Gnat was selected for the IAF in 1954, whilst in development at Folland, UK. It was a bold decision. A senior test pilot (Suranjan Das) was seconded to Folland to assist in development of the aircraft. Aside from India, the only other country interested in the Gnat was Sweden (they purchased 12 aircraft). A small team of senior IAF officers was also deputed to Folland to oversee development. The first Gnat came to India in Jan 1959 ; it flew in the Republic Day Flypast.
2. The Handling Flight formed in Dec 1959 with 6 Gnat aircraft, 4 pilots, 1 engineer officer, around 50 airmen and 10 lascars. It formed the “B” Flight of A&ATU, Kanpur, under the command of Wg. Cdr. Suranjan Das ; its tenure was one year. Its main tasks were:–
(a) to recomend spares, required for future Gnat squadrons.
(b) to verify the Gnat’s capability to perform ground-attack missions (guns,rockets, bombs).
(c) to verify performance of its fuel-dip system, which enables complete fire-out of its guns at 45,000 ft.
3. These were simple tasks for a developed aircraft. Unfortunately a number of aircraft-systems proved to be faulty. Four such systems are mentioned below :–
(a) The most serious and complicated fault lay with its slab-tail control,the Hobson Flight Control Unit (a larger version performed well on the twin-engine Lighting aircraft).
Two test pilots had been killed ; one at Kanpur in early 1959, the other at HAL, Bangalore in 1960.
Wreckage examination revealed the slab-tail was in the ‘full nose-down position’, whilst the pilot’s control column was in the ‘full nose-up position’. This could only happen if there had been a ‘trim runaway’.
Numerous mods were introduced, with switches in the cockpit to isolate the FCU. The cause of failure was never established. The last accident of a similar nature occurred at Pathankote in Nov 1971.
The Bouche Committee recommended several measures, which were physically incorporated by HAL, under their Chief Designer Mr. Vardarajan. This was achieved in the mid-1970’s. No further failures took place.
(b) Malfunction of the Glouster fuel-flow proportioner (due to deterioration of rubber components). Flame out by two aircraft in 1960 was probably due to fuel starvation, caused by fuel-flow proportioner malfunction. When drop tanks were carried and improper fuel-flow occurred, the c of g moved aft, making landing hazardous. Drop tanks had to be jettisoned, before landing.
(c) Failure of rubber seals in the hydraulic system. After a case of blockage of the filter in the starboard aileron servodyne, leading to the control column jamming in the fully port position (the pilot had followed the ’emergency drill’ specified in the Company’s Pilots’ Notes ; the aircraft had reached landing-flare-out height at Palam’s RW 33, when the emergency arose). The PN’s were immediately amended and one more mod introduced, whereby the pilot could select manual aileron control instantly (both aileron servodynes hydraulically blanked off).
(d) The radar ranging system was unreliable ; proved during trials at Jamnagar A/A range in Apr 1961. Manual ranging of the GGS was most successful against banner-towed-targets.
4. In Apr 1960, the Flight ceased air operations for 5 months. All Gnats of A&ATU underwent an improvement mod programme. The tenure of the Flight was extended by 4 months to the end of Apr 1961.
5. Several mechanical problems rose in later years. Two are mentioned. (This author had been closely connected with Gnat operations). (a) Gun stoppage, due to faults in the cross-belt, gun feed system, occurred during the 1965 war. Pak aircraft, escaped being shot down.(b) Breakage of the undercarriage radius rod, during the landing-run, caused violent pitch-up and the aircraft went off the runway.
6. The Handling Flight generated spares consumption data. It verified the aircraft’s capability to perform all ground attack missions (guns, rockets, bombs) at Tilpat A/G range. Its fuel-dip system was proved to be efficient during gun-firing trials at 45,000 ft at Jamnagar A/A range.
7. In conclusion, the Gnat was most effective in the wars of 1965 and 1971, but it was ‘accident prone’ throughout its ’30 year-service-life’.