Loss of A4G Skyhawk 875

[Luig]

RAN FAA TOUCHDOWN Magazine 3/97

Looking Back - A Bad Month for the Bean-Counters!
by CMDR John Crawley, RAN (Rtd)

0n the 2nd October 1980, VF 805 Squadron Skyhawk N13-155062 (875) suffered an engine failure during a catapult launch from HMAS MELBOURNE in the Andaman Sea, 35 nm north of Sumatra, Indonesia. The pilot, fortunately, was able to eject and was rescued by 'Pedro', the SAR helo. The aircraft sank in 1,279 metres of water in position 5° 49.6' N, 96° 38.5' E and was lost.

Skyhawk 875 was the first of two Skyhawks to be lost off the same catapult during the same month. On the 21st October SBLT David Baddams also ejected, this time into the Indian Ocean 100 nm southwest of Colombo, Sri Lanka escaping with only minor injuries after his aircraft, N13-154-906 (885), received a 'slow' catapult shot.

These two launch attempts proved to be among the last at launching Skyhawk aircraft from HMAS MELBOURNE [885 was the last A4G catapult]. The ship was to later go into refit and shortly after in early 1983 the new Federal Government announced the intention to cease fixed-wing flying in the RAN and dispose of the aircraft carrier.

The following account of the loss of the first Skyhawk, 875, is from an interview with CMDR Clive Blennerhassett and the Board of Inquiry (BOI) Report.

At 1708 hrs local (GH) on the 2nd October 1980, Skyhawk 875 was recovered onboard HMAS MELBOURNE following a normal training sortie. The pilot for this sortie was Captain Tom White, USMC. Following the landing, the aircraft was positioned for an engine-running or 'hot' refuel prior to the next launch. Captain White remained in the aircraft during the refuelling operation and then handed the aircraft over to [the then] LCDR Clive Blennerhassett, Commanding Officer of VF805 Squadron, and pilot for the next sortie. (Clive is known universally as simply BH.) Let's begin with his account of the final flight of 875.

The pilot's report
I was briefed for an INTEX/DLP sortie with LEUT Andy Sinclair. I was due to take aircraft 876, but it became unserviceable and so it was arranged for me to to do a hot fuel and hot pilot switch with one of the Skyhawks that was already airborne. That switch was due to occur at 1705. Andy manned his aircraft and launched at 1645 or thereabouts and I waited for my aircraft to arrive back.

About five or ten minutes later I went down to the deck ready to get in the aircraft, and I suppose it finished its hot refuel (4,600 lb) about five minutes later. Captain White climbed out of the aircraft and I climbed in. I strapped in, turned all my avionics on and then just sat there for a while and made sure that everything was up and running okay. I then went through a TAFFIOHHHC check while I was still in the chocks, which is a very comprehensive check for take-off flight actions. Once I'd completed that I called 'On deck'. Almost immediately I was taxied forward to the catapult and into the chocks, and was loaded on the catapult without any problems.

Virtually as soon as I was tensioned up, I was told to go to full power, which I did and achieved full power. The EPR provided earlier was 2.42 which agreed with the EPR on my gauge, oil pressure was just above the lower limit at 41-42 psi, EGT was 650°C and rising, oil quantity was 20-80 per cent, trims were indicating 6° nose-up and zero rudder, and flaps were full down. I checked the fuel control panel - the aircraft was in primary fuel control, drop tank pressurisation was off, as was emergency fuel transfer. I lowered the catapult grip, wound up full friction on the throttle and saluted the FDO - and away I went!

The launch felt quite normal and the aircraft rotated normally off the end of the ship, but at that point I noticed that everything suddenly went very quiet and my rate of acceleration reduced quite markedly. I was looking out at that stage adjusting the aircraft attitude and when I looked back inside the cockpit I noticed the RPM gauge winding down through 72 per cent or thereabouts – this was merely an observation of the main needle, a position rather than a physical reading.

[Very soon after the launch an abrupt reduction in noise was noticed by several witnesses. A few witnesses also noticed unusual noises during the catapult launch. The precise point at which the reduction in noise and other unusual noises occurred could not be determined by the BOI, but the evidence pointed to approximately halfway through the catapult stroke.]

Time to go
So I elected to eject – probably about two seconds after I realised something was wrong. I ensured the aircraft was in a nose-high position – and I had plenty of elevator control to achieve that – but I felt that the aircraft was sinking. I reached down with my left hand and pulled the seat pan handle. Next, I saw the canopy go and almost immediately the seat fired. It was a reasonably gentle ride up while I looked down and saw the A4 'sinking' underneath me. I tumbled in the seat a couple of times before ending up facing backwards along the shroud lines. I saw the parachute streaming but not inflated. I then turned around again to face forwards at which point the parachute canopy ballooned with a reasonable but not large shock . I did not see the ballistic [parachute canopy] spreader fire.

I don't recall the remainder of the descent into the water. My next recollection is of hitting the water and submerging two or three feet. I floundered to the surface confused but I had no trouble staying afloat even though my Mae West was not inflated. The parachute had collapsed by this time, so I searched for and found the actuating handle for the Mae West and it inflated okay.

I was worrying heaps about sharks at about this time until I realised I was having trouble breathing. I tried to get rid of my oxygen mask but the stoles on my Mae West had inflated to such a degree where they were bearing against my chin and I was having difficulty reaching the mask fastening clips . I eventually got the right clip unfastened and pulled the mask away from my face. What a relief – but just then the bow wave from the ship hit me and I went under again gulping in not air but sea water!

A lot of things started happening about this time. I saw a ship making for me (the rescue destroyer), Pedro (the SAR helo) was hovering nearby, I was coughing up sea water, the parachute 'Koch' fittings were proving a little tricky to release, and finally, I got hit by the ship's stern wave as well – another sea water gargle!

I think I shed the parachute as the SAR diver (Leading Seaman Rick Newman) jumped from the helo to assist me. I owe that guy heaps, he jumped into a known shark-infested area to assist me. After ascertaining that I was reasonably okay, and after a rather fruitless attempt to partially deflate the over-inflated Mae West, Rick wrestled me into the winching strop. From here it was clear sailing and after Rick was winched up we landed back on board the carrier for the mandatory medical check. Total time from 'go' on the catapult to landing back on board was only four minutes - but it seemed much longer!

[Skyhawk 875 sank a few seconds after impact and, although HMAS PERTH was quickly on the scene, nothing of value was recovered. The only items salvaged being a piece of the aircraft's radome, the pilot's parachute and a small plastic bag containing air navigation publications .]

What caused the accident?
The BOI (CMDR (P) David Farthing, LCDR (AE) Roger Colless and LEUT (P) Terry Ford), assisted by ship's staff, carried out an exhaustive analysis of the accident. This was a commendable effort considering the environment and circumstances prevailing, an effort duly recognised and acknowledged by higher authority.

The BOI considered the full gambit of possible causes:

• sabotage;

• human error;

• catapult malfunction;

• environmental conditions (eg, sea state, weather);

• catastrophic mechanical failure within the aircraft's engine;

• fuel contamination;

• Flight Control System (FCS) malfunction; and

• accessory failure.

1. Sabotage was quickly eliminated, particularly as the aircraft had just completed a mission prior to the hot refuel.

2. Human error. After an exhaustive review of aircrew and maintenance personnel and procedures, human error was also eliminated as a factor in the accident.

3. The ship's catapult performance was often open to question. Although steam-operated, it was of a very dated design and which experienced its fair share of mechanical breakdowns during any cruise and usually required much work during ship refit periods. However, whilst the catapult was to feature significantly in the loss of 885 later in the month, it was proven to have performed satisfactorily during 875's launch. Catapult records revealed that the end-speed ordered for the aircraft (at a launch weight of 15,800 lb, wind 0-2 kts, ship speed 20 kts) was 113 kts. The end speed actually achieved was 111 kts. However, as the aircraft's engine thrust usually contributed 3 per cent (or 3.3 kts) to the end speed, the loss of 2 kts end speed during 875's launch was attributed to the loss of some engine thrust during the catapult stroke.

4. Weather and sea state at the time of the accident were summarised as little or no wind, calm seas and fairly high ambient air temperatures. At the time of launch, wind over the deck was about 22 kts, comfortably in excess of the required minimum for this particular launch of 16 kts.

5. Catastrophic mechanical failure within the engine was also discounted, as :

• oil pressure was normal throughout the period of applied military power (12 seconds) prior to launch;

• no visible foreign matter, flames or sparks were observed from the aircraft exhaust;

• no aural indication of compressor, turbine or bearing failure was heard by witnesses or the pilot; and

• the smooth engine run-down noise was heard by several witnesses adjacent to the catapult track.

6. Fuel contamination. Much time was spent on eliminating fuel contamination as an accident causal factor. The reported extremely slow rate of fuelling of 875 immediately prior to launch raised suspicions in this regard . However, rigorous testing of the ship's AVCAT [JP5] fuel system (and sampling other embarked fuelled aircraft which all produced satisfactory results) discounted fuel contamination as a causal factor.

7. FCS system. The aircraft was in a clean, symmetrically loaded state with approximately 4,900 lb of fuel at launch. C of G was 23 per cent of Mean Aerodynamic Chord (MAC), well within limits. Further, the pilot reported the aircraft as fully controllable up to the time of ejection with no unusually large stick forces or control deflections. An FCS malfunction was thus disregarded as a primary or contributory cause of the accident. [(A)FCS = (Automatic) Flight Control System]

8. Accessory failure.
Evidence strongly suggested that the engine started winding down during the catapult stroke and there was some evidence of an unusual ' thud/clunk' noise occurring during the stroke. The only accessory failures which the Board considered could cause a sudden degradation of power without accompanying major breakdown of engine rotating assemblies were those components in the fuel supply system, ie:

• a Fuel Control Unit (FCU) malfunction;

• a throttle linkage failure;

• an engine-driven fuel pump failure;

• a manual fuel shut-off valve closure; and

• a fuel line rupture.

Simulating the accident scenario
The Board considered that whatever failure may have occurred, happened at or shortly after the beginning of the catapult stroke. Attempts were made to simulate the effects of the above accessory failures by positioning a Skyhawk on the catapult and carrying out the following:

• a snap closure of the throttle from military power to idle, which resulted in an RPM decay to 70-75 per cent within 1.5 seconds;

• switching from primary to manual fuel control while at military power, which resulted in a minor 'thump' similar to, but less pronounced, than the normal pre-take-off manual check at 85 per cent RPM, with fuel flow dropping slightly;
and
• a snap closure of the manual fuel shut-off lever with the aircraft at military power. This resulted in the engine continuing to run at military power for about three seconds, with RPM then slowly decaying to about 70 per cent over the next five seconds, followed by a continuing decay as in a normal shutdown.

The final few moments
Projection of the line-of-flight of the aircraft from photographic records indicated that the aircraft maintained near straight-and-level flight. If the aircraft was projected at the same speed ballistically, it would have entered the water within two seconds, even allowing for some glide capability. Additionally, the pilot reported that the aircraft was still quite controllable at the moment of ejection, indicating that the aircraft was still well above the low-power stall speed of 110 kts at its launch weight. This suggested that the engine was still developing some thrust during the first moments of flight, further substantiated by the SAR helo pilot's observation of a brief jet efflux disturbance on the sea ahead of the ship.

From the foregoing, the Board considered that failure of the engine-driven fuel pump was unlikely as was partial or complete closure of the manual shut-off valve following a linkage failure and/or subsequent acceleration loads. (The geometry of the linkages and the valve itself did not favour such a closure under acceleration loads.)

That strange 'thud/clunk'
The Board considered the following possibilities regarding the reported noise during the catapult stroke:

1. An uncommanded switch to the manual fuel mode within the FCU, producing a noise similar to that obtained during power trials on the catapult. Such a switch would undoubtedly indicate a FCU malfunction leading to loss of fuel pressure/flow and a subsequent thrust loss.

2. Mechanical failure, either within the fuel feed system or elsewhere. Although an unrelated mechanical failure could not be ruled out, any mechanical failure generating a noticeable noise would almost certainly be related to the power loss. The Board felt that if an audible mechanical failure did occur it was within the fuel feed system, but in the absence of further evidence they could not be more specific.

3. Catapult or other spurious noises. Although ship-generated noises would be more audible with the reduced jet blast noise apparent during the launch of 875, the witnesses reporting the 'thud/clunk' noises were sufficiently experienced on deck not to be unduly distracted by such normal, but more audible, noises. In particular, the catapult director was certain that the noise emanated from the aircraft.

4. Loose objects (FOD or otherwise). Although such a possibility could not be discounted, the Board felt that as :

• the aircraft had already flown at least one sortie since any access to internal compartments or internal work had occurred;

• no anomalies in the squadron tool control organisation or accounting were apparent; and

• the pilot did not notice any sound or feel anything unusual during the catapult stroke;

the reported noise was unlikely to have been caused by loose object movement.

Looking at the throttle linkage
A Skyhawk throttle linkage system was examined and the Board considered that failure within this system was a distinct possibility. A linkage failure at the FCU power lever would almost certainly result in a power loss during the catapult stroke as forward acceleration would move the unbalanced lever towards the idle position. This possibility was further substantiated by the following:

• military power was being developed at the moment of launch;

• engine wind-down was evident during the catapult stroke; and

• indications of some residual power suggested that total fuel starvation had not occurred.

Fuel line rupture was considered improbable due to the lack of physical evidence of spilling fuel. Such a failure between the engine-driven pump and the FCU would lead to an almost instantaneous shutdown. Failure between the manual shut-off valve and the engine-driven pump was also considered improbable for similar reasons. Significant fuel line rupture further back in the fuel feed system would almost certainly have spilled sufficient fuel on deck or into the aircraft slip stream to be visible to the many witnesses of the launch and, furthermore, the engine would have run for several seconds before power loss occurred. The squadron maintenance chief (CAA) [Chief Airframe Artificer] reported that, from records and squadron maintainers' recollections, no abrupt power losses had ever occurred during engine trim or other base runs to military power with Skyhawk 875.

Cause of accident
The Board concluded that the accident was caused by a significant loss of engine thrust as, or soon after, the catapult fired and this thrust loss was attributed to a fuel system malfunction. In the absence of actual physical evidence the precise nature of the malfunction could not be determined; however, the cause was deemed to be (in order of most likely) either:

• an FCU failure;

• a throttle linkage failure;

• an engine-driven fuel pump failure;

• a manual fuel shut-off valve closure due to mechanical failure; or

• a fuel line rupture.

The Board noted that HMAS MELBOURNE's records show that there had been 8,834 A4 Skyhawk launches since 1969. As far as could be determined, no previous unexplained cases of abrupt power loss during the catapult stroke had been experienced nor had any abrupt power losses occurred during full-power base runs. They were well aware that in the absence of definite physical evidence, their findings were, to some degree, speculative. Nevertheless, after thoroughly considering the available evidence, they recommended that this accident be regarded as 'an isolated case of fuel system malfunction '.

Board observations
1. Safety Equipment. The pilot expressed concern about his minor injury from the closure plate of his LPA-2 life preserver. He thought that a higher-speed ejection could have resulted in a more serious injury. Previous investigations into this matter had attributed such injuries to incorrectly fitted torso harness/LPA-2 assemblies. All Skyhawk aircrew were briefed at that time to have their fitting checked and LCDR Blennerhassett had, in fact, been measured and fitted with a new harness.

2. Apparent over-inflation of life preserver. Both the pilot and the SAR diver commented on the difficulties experienced with the almost rigidly inflated LPA before and during recovery, leading to:

• difficulty in removing the oxygen mask;

• the pilot unable to reach or activate oral valve;

• problems with locating and releasing parachute Koch fitting;

• difficulty in locating survival pack release fittings and oxygen hose attachment; and

• assistance required to enter helicopter strop.

This post has been edited by Luig on Oct 6 2013, 07:12 AM

[Dave Masterson]

Thanks Phil.....it makes for interesting reading :D