PTT, Dave Un­win

Pilot - - CONTENTS -

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

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