Air Safety — They Can Turn and Bite

But what could be the explanation for these accidents when the stalling characteristics of high wing Cessnas seem so innocuous — and the aircraft types’ general handling so demonstrably docile and viceless? In any case, the pilots concerned would surely have been mindful of their stalling speed — the aircraft’s unmistakeable audible stall warnings would see to that. So why were they not heeded in time to prevent the loss of control — if indeed that was the problem?

Let’s look at a few typical case histories:

A Cessna 175 carrying a crew of four was engaged in a shark patrol over beaches in Port Philip Bay, Victoria. Flying at about 600 feet, the crew sighted a shark in the shallows close to where a number of people were swimming. Lowering 20 degrees of flap, the pilot rolled into a descending steep turn to circle over the shark. During several progressively tightening 360° turns, the angle of bank steepened to about 70° and the aircraft gradually lost height. Then the nose suddenly dropped sharply and the aircraft plunged into a spiral dive towards the water. The pilot achieved a degree of recovery, but it struck the water still in a nosedown attitude. One passenger received fatal injuries and the pilot was seriously injured. Neither the pilot nor the surviving passengers could recall hearing the stall warning before the aircraft fell out of the steep turn.

At a Nsw country airport, a visiting pilot was demonstrating a Cessna 172 which he hoped to sell to the local aero club. Two young student pilots accepted his invitation to accompany him on a flight, and the aircraft taxied out. Minutes later, other pilots in the clubhouse saw the aircraft takeoff into the west, and after climbing to about 500ft, it performed a wingover to the left and dived back towards the strip. Easing out of the dive, it made a fast downwind run over the strip at about 400ft. Soon after crossing the eastern airfield boundary, it pulled up into a steep climb to 300 or 400ft, then carried out what appeared to be a stall turn to the left. But there was no recovery from the resulting dive and, still 60° nosedown, the aircraft struck the ground some 700 metres beyond the end of the runway. All on board were killed instantly.

The pilot of a Cessna 175 was taking four children for a local flight from a station property airstrip in South Australia. Flying over the station homestead at a height of about 200ft, the aircraft rolled into a progressively tightening steep turn around the house as the passengers waved to their parents on the homestead lawn below. As the turn continued to tighten and the angle of bank steepened, the aircraft nosed down, finally diving out of view of those watching in a near vertical bank and a steep nosedown attitude. Almost immediately there was a noise of violent impact and dense black smoke rose from beyond the house. All on board the aircraft were incinerated.

On a hot day with little wind in western Nsw, a Cessna 172 was taking off from a station property airstrip. On board, in addition to the pilot, were three adult male passengers. The aircraft’s load would have been close to the type’s maximum permissible weight, and the pilot had not made any load chart calculations taking into account density altitude. The takeoff itself seemed perfectly normal for the conditions, with no excessive run before becoming airborne, but as the aircraft climbed away, it encountered a patch of thermal turbulence, causing a moderate wing drop. As the pilot appeared to be correcting the aircraft’s attitude, the nose suddenly dropped violently and the aircraft dived almost vertically into the ground. No fire broke out, but all on board were killed instantly.

At Inverell, Nsw, a moderately experienced private pilot had hired a Cessna 177 for a business trip to Grafton with one passenger. Not having flown a 177 before, he had the owner brief him on the type’s handling characteristics before departing. The day was hot with a gusty wind from the northwest and the pilot began his takeoff into wind on the northwestern strip. The aircraft became airborne after a run of about 500 metres and began climbing normally. Some 700 metres after lifting off, at a height of about 200ft, it began a gentle turn to the left. As the turn continued however, the angle of bank suddenly steepened, apparently as a result of a gust, the nose dropped, and the aircraft spiralled steeply into the ground and caught fire. The pilot was killed, but the injured passenger managed to extricate himself from the wreckage before the fire took hold.

A Cessna 172, based in northern Tasmania and flown by an experienced commercial pilot, was making a charter flight to Smithton from Three Hummocks Island in Bass Strait, carrying three passengers. The wind was blowing hard from the northeast, gusting to about 25 knots (45km/h). Lined up into the north, the pilot lowered 20° of flap, then applied full power while holding the aircraft on the brakes. When the brakes were released the aircraft rapidly gained speed, lifted off normally, and climbed quickly to about 70ft. At this height it appeared to be affected by the strong crosswind, the aircraft yawing into wind as the pilot apparently compensated for its effect. Still attempting to climb quite steeply, and buffeted by the turbulence, the aircraft then momentarily lost height. At this point the port wing dropped sharply, and the aircraft dropped into a steep spiral dive, striking the ground in a patch of thick scrub. This fortunately cushioned the impact, and all four occupants, though injured, survived. One of the passengers said the stall warning was sounding continuously throughout the takeoff.

At an informal flying school “picnic day” at a country airstrip, a young flying instructor announced he would “demonstrate the Aerobat” — the school’s Cessna A150. Taxying to the threshold, he lowered almost 30° of flap and opened the throttle for takeoff. After only a short run into the eight knot (15km/h) breeze, the aircraft became airborne at low flying speed in a marked taildown attitude. Climbing steeply to about 200ft, the pilot levelled out and retracted the flap. The aircraft then banked into a tight turn to the right until it was heading back towards the airstrip, and began to dive, levelling out on a downwind “beatup” of the strip at high speed. As it approached the end of the strip it abruptly nosed up again into a steep climb, the speed progressively falling off again as the aircraft rapidly regained height. When it reached about 300ft, the nose suddenly pitched down, the port wing dropped sharply, and the aircraft began turning to the left. The engine noise ceased and, with the aircraft still turning, its nose continued to drop until it was diving steeply towards the ground. Although its speed built up quickly again, the aircraft showed no sign of recovering before it disappeared from view behind trees.

Moments later those watching heard the unmistakable sound of impact. The pilot was killed instantly.

In addition to these representative accidents, a number of similar ones, all involving Cessna 150 series aircraft, have occurred during aerial mustering operations on large pastoral properties. The pattern of events leading to these accidents is almost identical — low level, low speed flying involving dives, steep climbs, and tight turns, all accomplished by coarse use of the flying controls as the aircraft was being positioned to “get the stock moving”. During the manoeuvres, and apparently without obvious aerodynamic warning, the aircraft have suddenly flicked into a near vertical dive from which there was no hope of recovery in the height available. For the pilots concerned, the result has consistently been fatal.

Why, it has to be asked again, have all these aircraft plummeted nearly vertically when the usual result of a deliberate stall is little more than a gentle nodding — easily checked with power and airspeed? Could the high wing Cessna design possibly be a “wolf in sheep’s clothing” after all? If so, what could be the trigger for this covert syndrome to assert itself so suddenly and unexpectedly?

Clearly, in all the cases cited, the flight conditions, or the pilot’s use of the flying controls, exceeded the operational limits within which the aircraft was designed to be flown. Operated within these parameters, these aircraft are most certainly viceless and gentle, with an entirely predictable control response. But like most docile, well behaved creatures when too many liberties are taken with their desirable features, they can — and will — turn and bite, as the pilots of the aircraft mentioned tragically found to their ultimate cost.

Unfortunately, human nature being what it is, it seems that there will always be pilots who, despite the best endeavours of flying training organisations to inculcate sound principles of airmanship, will take liberties with whatever type of aircraft they fly, even in basic manoeuvres.

Back when the first new Cessna 172s took private flying in Australia by storm in the early 1960s, I well remember encountering four members of an aero club from a southern city at a country aerodrome where I had landed in the course of an aerial work operation. They were taking their club’s newly acquired 172 on an extended trip and, when I showed an interest, were loud in their praise of its wonders.

“Hop in,” one of them insisted after some of this talk. “I’ll show you how safe it is!”

Unwisely I did so, but soon had cause to regret my foolishness. Taxying to the threshold of the into-wind runway, this club pilot lowered some flap, opened the throttle and, waiting only until the aircraft had gained a minimum amount of flying speed, hauled it off the ground with the stall warning sounding. He then proceeded to climb out in steep noseup attitude, still with the stall warning blaring continuously, until we had gained about 500ft. I was unimpressed, but being completely unfamiliar with Cessna types at that stage, had no way of assessing the margin of safety inherent in such a manoeuvre. It is a tribute to the Cessna’s design characteristics that the only negative result of this performance was my resolve to never again fly with a nonprofessional pilot whose standards I knew nothing about.

Knowing what I know now, I believe our safety (and probably our lives) were balanced on a knife edge. Encountering a sudden gust, or the coarse use of rudder for any reason during that heart-in-mouth climb, could have immediately produced that same near vertical dive that has killed so many unfortunate pilots and their passengers, with no hope of recovery in the height available.

The little known truth of the matter is that the aircraft type does not have to be in an apparently incipiently stalled configuration (ie with the stall warning sounding) for such a loss of control to occur. In certain unusual configurations of low airspeed, high angle of attack, power-on flight, all that is necessary to precipitate a dramatic loss of control, followed abruptly by a near vertical dive, is a coarse misuse of the flying controls.

This is what one experienced mustering operations pilot had to say about the phenomenon following a spate of three very similar Cessna 150 mustering fatalities. His pungent comments on aircraft handling apply equally to any who feel tempted to put on an impromptu “display” involving similar manoeuvres at low altitude:

Aerial mustering was introduced to combat rising labour costs and a shortage of experienced stockmen. The aircraft is usually flown at 100-300ft at around 60 knots (110km/h) with 10-20° of flap selected. Communication with stockmen on the ground is by two way radio. When stock are spotted the ground crew are called in and the aircraft dives to indicate their exact position.

Three recent fatal mustering accidents have much in common. All were found in virtually identical attitudes; all appeared to have struck the ground in a vertical dive; and in each case it seems the aircraft stalled while manoeuvring at low level. I believe all three accidents were caused by a little appreciated handling characteristic which, though no problem at safe altitudes, can be extremely dangerous at the low heights common to mustering flying.

In each of these three cases, the aircraft was probably climbing away after a dive at about 80 knots (150km/h) with nearly full throttle. Before levelling out, a steep turn was probably begun with the nose still up about 15°. I believe that instead of allowing the nose to drop away, the pilot, who would almost certainly have been looking back at the ground, continued to hold on up elevator until, with the steep angle of bank, the aircraft stalled. The “outside” wing would have stalled first and the aircraft would have flicked out of the turn in the opposite direction and pitched vertically nosedown. In a Cessna 150, this vertical nosedown attitude that follows a stall off a steep climbing turn occurs very quickly and recovery to level flight takes about 400ft.

The three fatal mustering accidents fall into a category entirely on their own. The common factors are that there was no failure of the aircrafts’ systems, no obvious terrain hazards, and all struck the ground in the same vertically nosedown altitude. It seems to me that it is this “unknown” characteristic that is claiming these lives.

Stall behaviour varies from aircraft type to aircraft type, but in every case a gentle straight ahead stall at a safe height practised during training is a vastly different matter to loss of control in an extreme attitude with power on near the ground. In these situations, even the most docile aircraft can bite. Above 3000ft, the loss of height needed for recovery is barely noticeable. But at low level, the consequences of a violent stall can have only one result!

Still not convinced? Well try this for yourself sometime: Take any high wing Cessna, together with a flying instructor (or competent safety pilot well experienced on the type), remove or secure any loose equipment, and fly to a training area where you can climb to a safe aerobatic height. After clearing the area around and below you in the usual way, set the aircraft up to maintain slow speed, high angle of attack level flight. This can be achieved somewhere between 45 and 60 knots (85 & 110km/h), according to aircraft type and performance, usually with around 1600-1700rpm, or about 16 inches of manifold pressure if the aeroplane has a constant speed propeller. Use no more than 10° of flap.

When the aircraft is fully stabilised in this flight regime and you and your safety pilot have the feeling you could go on flying this way for hours on end, ensure again that your seat belts and lap straps are snug, then smoothly but quickly apply full rudder — say to the right — without moving the aileron controls. The result may surprise you. It will also help your understanding of how these accidents developed. Best of all, the experience could just one day save your life.