PTT, Dave Unwin
More ‘practising bleeding’ — the perils of simulated engine failure in training exercises in airliners
My PTT about ‘practising bleeding’ ( Pilot, June) generated an interesting criticism from an old flying mate, who quite rightly pointed out that as it referenced Canberras, Meteors, Typhoons and Vampires GA pilots wouldn’t think it was relevant. “Remember when spinning at low level was in vogue with the BGA?” he grimaced, “that was practising bleeding!”
He wasn’t wrong. Many years ago spinning off the top of a winch-launch wasn’t only in fashion, it was an operational necessity. Spinning was (and still is) an integral part of the British Gliding Association’s training syllabus, and as some clubs only winchlaunch and students had to have ‘spins satis’ in their logbook before going solo... well, it had to be done. However, although acceptable in a T-21 it was a bit marginal in a K-13, and decidedly dodgy in a Puchacz. It could still be done but the safety margins were slowly but surely being eroded. Curiously, even when aerotows became more widely available some older instructors still insisted on spinning at low level, arguing that students needed to experience the ‘ground rush’ effect.
This argument is not only fallacious, it’s actually stupid. If a full spin develops on the base-to-final turn there isn’t enough height to recover. Everyone knows that prevention is better than cure, and what students needed to be taught was spin avoidance, not spin recovery. Eventually, after several low-level spinning exercises ended in fatal accidents the practice was discontinued.
Turning back at low level after a simulated engine failure on takeoff can also be viewed as practising bleeding. It’s irrefutable that an accurately flown, tight 180 is perfectly possible with (depending on the aircraft) surprisingly minimal height loss. However, quite apart from the fact that you’re now landing downwind (with that situation’s myriad issues), demonstrating the turn-back never allows for the ‘startle factor’, and this plays such a fundamental part in the real thing that it renders the entire exercise invalid. Of course, there’s also a psychological aspect to demonstrating both turn-backs and low-level spins; some instructors love trying to demonstrate just how clever they are — a practice that can also end in disaster.
Even major airlines aren’t immune to such folly. When BA operated the 707 it was common for the training captain to chop a throttle at Vr. Now, a 707 is only a four-engined jetliner that, even on a training flight, weighs about 100,000kg and rotates at 140kt — what could possibly go wrong? As it transpired; plenty, and this practice was eventually discontinued after the inevitable and expensive accident.
Before the introduction of decent simulators the training captains of jet transports really earned their money. Any instructor, whether in a PA-28 or an MD82, knows it is imperative to allow the student to make mistakes — otherwise how will they learn? For all instructors, the real trick is not to let the student put them in a situation they can’t retrieve!
Training in piston-powered multi-engine aircraft, such as a Lockheed Constellation or Douglas DC-6, had many advantages over jets. Not only did the engines accelerate promptly but the propwash over the wings produced a phenomenon known as ‘induced lift’. This meant that, although the aircraft could be flying dangerously slowly, the wing was still producing lift when the engines were at full power. Consequently (and especially as training flights are flown at relatively light weights) the training captain could allow a low, slow approach to develop. Then, when all appeared lost, a big handful of power could save the situation.
However, jets such as the Douglas DC-8 and Boeing 707 possessed none of these advantages. The pod-mounted turbojets meant that not only was there no induced lift but they also took a long time (up to eight seconds) to accelerate from idle to full power. And, of course, even after the engines had ‘spooled up’, the aircraft still had to accelerate. From deciding to go around and adding full power, to the point where the aircraft would finally stop sinking and begin to climb, could take as long as ten seconds, more time than many pilots had left to live…
Perhaps unsurprisingly, jet transport flight training (and asymmetric training in particular) caused more accidents than actual emergencies. For example, a 707 was on final with one engine deliberately shut down when the flight engineer noticed the hydraulic fluid in one of the systems was getting low. Not wanting the pump to burn out, he shut it down, without first asking the captain to re-start the shut down engine. The hydraulic boost to the rudder was lost and the aircraft was instantly below Vmca (minimum control speed with an engine shut down), without hydraulic boost. The 707 rolled over and dived into the ground, killing everyone on board. Shockingly, a perfectly serviceable jetliner (remember, none of the systems had actually failed — they’d been shut down intentionally) and crew had been lost needlessly.
So the message of this month’s PTT is simple: don’t practice bleeding. The fundamental problem with demonstrating a spin or a turn-back at low level is there is no margin for recovery if anything does not go perfectly. And if you’re practising emergencies and a separate failure occurs within the aircraft’s systems, rectify the simulated failure first.
Everyone knows that prevention is better than cure... Jet flight training caused more accidents than actual emergencies