IS A SINGLE-ENGINE TURBINE SAFE?

The worst possible scenario for a single engine aircraft is an engine failure at night or over solid cloud.

The Eastern corner of Canada is a wild and rugged country, often covered with the infamous Newfoundland fog banks. It is not a friendly place to fly, particularly with a single engine.

Yet it was the Canadian Civil Aviation Authority which led the way with the certification of singleengine aircraft for IFR charter operations. It was a bold move and their decision was tested sooner than anyone would have liked.

A Pilatus PC-12 flying a scheduled service between St. John's Newfoundland and Goose Bay Labrador was over solid cloud and at top of climb at 22,000 feet when the engine oil pressure started falling. To save the engine the pilots reduced power and decided to try return to St. John's. But at 16,000 feet the engine quit altogether.

They contacted ATC at St. Johns for vectors to the nearest airport, a remote strip about twenty miles away. The "go to nearest" function on the GPS confirmed the lack of alternatives. Soon they were in the cold, clammy grey clouds, heading inexorably towards the unseen earth below. The crew briefed the passengers to brace for the trees to start crashing through the windscreen. And then, almost imperceptibly, the cloud turned to wisps and they saw the landscape flashing by less than 300 feet below the wings. Without no time left, they slowed to just above the stall and aimed for a tree-filled marsh. The engine and most of the left wing were ripped off the airframe by the trees.

At just 60 knots the crash was benign. In the cabin the only injury was a broken collar bone from a seat belt and the co-pilot broke his leg.

And so the question arises: was this accident a vindication or a condemnation of the approval of FAR part 135 IFR and night single engine air taxi operations?

Not surprisingly Pilatus claims a resounding victory in that, thanks no doubt to the low stall speed of just 61 knots and, in part, because of the high crash worthiness of the seats, which are designed to withstand a 23G impact, injuries were minimised. From the operator's point of view their faith was undiminished. Kelner Airways replaced the destroyed PC-12 with another and, by way of endorsement, one of the passengers involved in the accident was on the next PC-12 to Goose Bay the following day.

This accident remains the litmus test for single engine IFR charter. The only mitigating factor was that it did not occur at night but, due to the cloud cover, it would not have made much difference whether it was day or night anyway.

The crew and passengers were helpless victims to the inevitable failures that will occur in anything mechanical, even in that paragon of dependability, a PT-6. This engine has a mean time between in flight shutdowns of over a hundred thousand hours, so the chances of an engine failure are slim. In single-engine installations as in the PC-12, TBM and Caravan, this chance must be even lower due to the manual overrides of the fuel control unit and the unlikelihood of a pilot shutting the engine down as a precautionary measure.