Air Safety

Soon we were in and out of cloud, picking up a little rime ice on the leading edges of the wings and tail. I thought this quite normal for this time of the year (it was mid winter), but as the accumulation continued, I informed Flight Service we were descending to cruise at 7,000. We then continued through broken cloud with no further build-up of ice.

Reporting to Wagga at Murray River, I requested and was given an airways clearance to Canberra via Talbingo on the 246 radial at 7,000 feet. This was the route I preferred because of the reasonable forecast and the fact that we had an excellent tail wind.

Changing frequency over Talbingo, I called Canberra Approach. They confirmed the clearance and requested us to call at 30 miles in the normal manner. Thanks to the tailwind, we had a ground speed in excess of 200 knots and our ETI for this 48 nautical mile segment was only 14 minutes.

We had been flying through about five-eighths of cumulus, with the stars visible above us most of the time, indicating that the tops were not particularly high. But now there were patches of cloud above and below the aircraft. The cloud continued to thicken and soon we found ourselves in eight-eighths of cumulus; by now it was turbulent and raining hard.

The airframe ice began to accumulate again, though not enough to cause concern, and I turned on the propeller de-icers. Within five minutes, however, we were encountering quite severe turbulence and picking up ice at an alarming rate.

We were now about 30 nautical miles from Canberra, so I called Canberra Approach and requested a descent below 7000 as soon as possible, but on this track the controller was unable to clear us below the lowest safe altitude of 6,790 feet. By this time we were too far into the ranges to turn back-with the existing wind, doing so could only have made a difficult situation worse.

The ice had now built up to the stage where I was having difficulty maintaining height. As well, I had to keep the elevator controls moving to prevent them from freezing solid-the trim control was already quite immovable. The airspeed indicator was fluctuating wildly in the turbulence, but I brought the speed back as far as I dared to try and hold height. Around 110 knots the aircraft began to buffet, as though nearing the stall. At this stage, Canberra Approach identified us on radar, 28 miles south-west and, five minutes after my earlier request, I again asked for a descent. The exchange went something like this:

Aircraft: “How are we for descent now?” Canberra: “Report flight conditions. ” Aircraft: “Very cloudy-still picking up ice. ”

Canberra: “Roger. In another five miles you’ll be able to descend to 6,000. ”

Aircraft: “We’re having trouble maintaining altitude. ”

Canberra: “Further descent in two miles-confirm you are able to maintain altitude?”

Aircraft: “Negative-we’re down to 6,000 now. ”

Aircraft: “Left 6,000-just can’t maintain altitude. Can you vector us over lower terrain?”

Canberra: “7,000 feet is the lowest safe altitude in your area. ” Aircraft: “We’re down to 5,700!”

Canberra: “Radar position is 21 miles south-west of Canberra. ” Aircraft: “Now down to 5,600 feet. ”

Canberra: “Have you lost your identity on radar- confirm operations still normal?”

Aircraft: “Altitude 5,600 – no 5,500 feet: Have to declare an emergency-can’t hold that altitude. ”

Canberra: “I have an ident now-18 miles south-west on the 246 radial – you are now in the 6,000 foot terrain clearance area. Report altitude?”

Aircraft: “5,200!”

Canberra: Are you able to maintain 5,200?”

Aircraft: “We’re down to 100 knots and just on the stall!” Canberra: “Your position now 16 miles south-west of Canberra and you are coming into the 5,500 terrain clearance area-that gives you 1,000 feet above the highest terrain in that area. ” Canberra: “Position 12 miles south-west-you have another two miles to go to the 4,000 foot clearance area. ”

Aircraft: “Roger, 5,100 feet-we’re holding 5,000 now . . .

After several terrifying minutes, the controller was finally able to clear us for descent to 4,000 feet. At 4,500 feet we broke out of cloud – there were the lights of Canberra! It is impossible to convey the sense of relief the sight of them gave me!

There was still a lot of ice on the aircraft, and as we had been buffeting to a marked degree during the last minutes before we became visual, the stalling speed was obviously still high, so I made the final approach at 105 knots. We touched down safely.

All this had taken place within the space of about 20 nautical miles, demonstrating how quickly a situation like this can deteriorate.

Later, reconstructing those horrifying few minutes from our flight times, distances and altitudes, it seems that we must have scraped over the Brindabella range with only a couple of hundred feet to spare. This would have been about the time Canberra lost us on radar. Then, in the darkness and cloud, we must have edged past the northern face of Tidbinbilla Peak about 100 feet below its top – if we’d been even slightly south of track, I wouldn’t be telling this story!

Incidentally, apart from the man in the right hand seat, the passengers remained blissfully unaware of their narrow squeak!

What is there to be learned from this experience?

Certainly the weather had deteriorated unexpectedly in the area-it was found in fact that a minor trough had formed, but as no other aircraft had flown the route for some hours before, no

Sigmets had been passed.

Should the accumulation of ice earlier on the flight have given some warning of the impending danger?No doubt some will say yes. But pilots with experience of these routes in winter know some ice accumulation is normal.

The real lesson concerns the selection of the route in such conditions – the time lost by taking a more westerly track over lower country would have been no more than that lost by the lower airspeed resulting from icing!

And certainly it would not have accumulated so many grey hairs!