High Level Navigation - Tony Cunnane's Life and Times

On 1 February 1967, just 3 weeks before the end of my basic flying training at Leeming I went off on a solo high level navigation exercise in Jet Provost Mk 4 XS218. My route was Leeming – Carlisle – Turnhouse (Edinburgh) – Acklington – Leeming. I was planned to fly the route at heights around 29,000 feet (For the benefit of readers who are not familiar with Flight Levels and Standard Pressure settings, I'll refer to heights in feet throughout this anecdote.) The climb was uneventful. Everything in the aircraft appeared to be working normally, engine, instruments, fuel consumption, oxygen flow meter and oxygen mask connections. As I mentioned in the last story, the Jet Provost Mk was unpressurised so I had to wear the oxygen mask throughout the flight and not go above 30,000 feet, the operating limit on the oxygen system.

All was well for a while but I could see an extensive bank of high level cloud getting closer – evidence of the warm front that the Met Officer had mentioned at the morning briefing. That was not a problem because I had passed my Advance Instrument Flying Test several weeks earlier and so I was qualified to fly in cloud (IMC – instrument meteorological conditions). In any case it looked as though the tops of the cloud were below the height at which I was flying.

As I neared Carlisle I spent some seconds checking my map and flight plan because I needed ATC permission to change heading and height for Turnhouse. Suddenly, the Controller at Boulmer radar station called me to ask if I had contact with a civil aircraft in the Upper Airway crossing my path from left to right on a heading of 060 degrees at 31,000 feet. I looked out and was surprised to find that I was now flying in and out of the tops of the cloud. I couldn’t see the reported aircraft and told ATC that I had no contact but that I was close to cloud. ATC did not answer that call. Then, a few seconds later ATC came up on the radio again, rather more urgently, and reported that the conflicting aircraft was now passing directly in front of me, still at 31,000 feet, still heading 060 degrees. Once again I said that I had no contact but with a reported height separation of 2,000 feet I was not alarmed. Again ATC did not reply.

All of a sudden, some instinct warned me that all was not well. I felt hot and slightly dizzy. I noted in great surprise that I was now flying in the cloud at 31,000 feet. Somehow, without realising, I had climbed 2,000 feet to the same height as the conflicting aircraft and I saw that I had wandered off course by about 40 degrees – to roughly the same heading as the invisible civilian aircraft. My first worry was that I was now flying without permission in the Upper Airway – a serious offence. More importantly, and more worrying, I seemed to have interpreted ATC’s information about the civilian airliner as an instruction to me to turn and climb. I must also have increased power to keep a constant airspeed in that climb although I had no recollection of having done so. Because of my sessions in decompression chambers, I recognised the symptoms of oxygen lack. I checked that my oxygen mask was still correctly fitted, that the hose was securely connected and that the rotating blinker on the oxygen regulator correctly blinked white and black alternately as I breathed in and out. I had to descend - and quickly.

A third time ATC came up on the radio, this time in an urgent voice asking for a radio check. The controller by then would have seen on his screen that I had changed heading and from his height finder he would know that I had climbed above my allotted flight level. I realised then that I had not been pressing the press-to-transmit button when I had supposed I was replying to ATC. The controller knew from my call sign, Romeo 32, that I was a solo student from Leeming. The subsequent conversation went something like this, as best as I can remember it:

"This is Romeo 32 – sorry about that - I’m not feeling well. There’s something wrong. I’m now at 31,000 feet IMC, heading 030 degrees. Where’s the other aircraft."

"Don’t worry about him, he’s well clear now. Have you checked your oxygen?"

"Affirmative – it looks OK – connected and flowing but I think I'm hypoxic." Actually I used the word anoxic for reasons explained in the previous chapter.

"Can you safely descend on your present heading."

"Affirmative."

"OK Romeo 32, maintain your present heading and commence a slow descent - and call me every thousand feet."

In that manner I descended, reporting my height every thousand feet. I came out of the high level cloud at about 15,000 feet where once again visibility was almost unlimited with the east coast and North Sea spread out before me. I began to feel much better. The ATC controller told me that instructions from my instructor at base were to proceed direct to RAF Acklington, the RAF’s No 6 Flying Training School in Northumberland, and land there. With occasional steers from the radar controller I continued my gentle descent and soon I could see Acklington. In due course I joined the circuit and landed without further incident, feeling completely recovered.

I was directed to park alongside a row of 6FTS Jet Provosts. I opened the canopy and an airman climbed up, as normal, to replace my ejection seat pin. I then got down from the aircraft to find a doctor was waiting to take me to Sick Quarters for a medical check.

While the doctor was doing his business a telephone message came through from the Flight Line Controller to say that the ground crew had found a fault on the airmix valve in the oxygen regulator in my aircraft. That meant that during flight I had been supplied with a mixture of air and oxygen instead of the 100% oxygen that was required for the high level part of my flight. Thus, once I had climbed above 25,000 feet I had become hypoxic and, without realising it, had started to fly erratically and even failed to press the transmit button when I was initially trying to talk to the radar controller. During the first part of the flight when I was under 25,000 feet, I had been perfectly OK. Once I had descended below 25,000 feet under the guidance of the radar controller, I quickly recovered without any ill effects whatsoever. (Log book extract below - click it for a full page)

After filling in a lengthy Special Occurrence Report at Acklington, I telephoned the controller at Boulmer to thank him for his assistance. It turned out  that he was a former Jet Provost flying instructor now on a ground tour. He told me that he had realised something was wrong and he had ordered the civilian aircraft to climb to 33,000 feet to avoid me.

When my aircraft had been refuelled and the oxygen regulator changed, I flew myself back to Leeming. As it happens, my very next trip, the following day, was my Final High Level Navigation test – which I passed with flying colours.

As pilots were wont to say, "I learned about flying from that!". The day you think you know it all is the day to stop flying.

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