Twin doesn’t equal safer

Pilot - - THE MALONE COLUMN - Pat­malone Pat has worked as a jour­nal­ist on three con­ti­nents and is a fixed-wing pi­lot and for­mer he­li­copter in­struc­tor with 1,500 hours TT

Like most read­ers of Pi­lot I’m an eclec­tic con­sumer of avi­a­tion prod­ucts. Or to put it an­other way, I’m a big tart when it comes to fly­ing stuff. I’ll get in any­thing if it goes up in the air: Tom­a­hawk to Ci­ta­tion via P-51, and Tor­nado to glider and hot air bal­loon−been there, done that. But of all the fly­ing things, my whole heart be­longs to the he­li­copter, be­cause it goes straight up, and side­ways, and back­wards, and be­cause there’s noth­ing else in avi­a­tion quite like fly­ing down to the pub for lunch. So this is about he­li­copters−but even if they’re not your bag, keep read­ing, be­cause it’s also about reg­u­la­tion, com­mon sense, and the fact that the price of fly­ing is eter­nal vig­i­lance.

We were all heart­ened when EASA em­barked on Rule Mak­ing Task 0318, which would re­visit the rules on sin­gle-en­gined he­li­copters fly­ing over ‘hos­tile’ ar­eas. It ac­cepted that en­gines are an or­der of mag­ni­tude more re­li­able than they used to be and there was no safety ba­sis for rules that al­lowed only twin-en­gined he­li­copters to fly over ur­ban ar­eas, over wa­ter, in the moun­tains or any­where that might re­sult in a dif­fi­cult forced land­ing. Progress at last. But we find that RMT 0318 has been ‘post­poned’ and, in­stead, ICAO has qui­etly em­barked on a re­write of its per­for­mance code for he­li­copters that could re­sult in all the world’s com­mer­cial op­er­a­tions hav­ing to be con­ducted in twins.

The im­pact on the he­li­copter in­dus­try would be im­mense. Twins are fan­tas­ti­cally ex­pen­sive to buy, op­er­ate and main­tain− they are the prov­ince of the mil­i­tary, the gov­ern­ment, and in­dus­tries like off­shore oil, where pock­ets are ap­par­ently bot­tom­less. And the rules on twins are based on an en­tirely false ‘safety’ premise.

To the lay­man, it stands to rea­son that they are safer than sin­gles. But in the last ten years there have been nine­teen fa­tal he­li­copter ac­ci­dents in the UK, which killed 62 peo­ple, and only one of those ac­ci­dents

was caused by en­gine fail­ure. The eight ac­ci­dents that in­volved twins killed 49 of those peo­ple. The only fa­tal­i­ties on the ground were caused by two of the twins. The main cause of ac­ci­dents is pi­lot er­ror, even among the most skilled and ex­pe­ri­enced pi­lots; those who fly twins. The Su­per Puma ac­ci­dent at Sum­burgh in 2013, which killed four, was due to vor­tex ring, ex­ac­er­bated by pi­lot con­fu­sion over the au­topi­lot. The EC135 that hit the Clutha pub in Glas­gow in the same year was starved of fuel, killing ten. There’s a case to be made that had the he­li­copter been a sin­gle, the seven peo­ple who died in the pub (eleven more were se­ri­ously in­jured) would have been saved be­cause it would have au­toro­tated, or at worst bounced off the roof−twins are high-en­ergy crash­ers.

The Su­per Puma that crashed into the North Sea in 2009, killing six­teen, suf­fered cat­a­strophic gear­box fail­ure, which brings into fo­cus the ma­jor prob­lem for twinengine­d he­li­copters. Re­mem­ber Bill Lear’s Lear Fan, which had two PT6 tur­bines feed­ing a com­bin­ing gear­box and a pusher pro­pel­ler? The claim was that it had twin-en­gined ‘re­li­a­bil­ity’ but none of the asym­met­ric thrust prob­lems of con­ven­tional twins. The FAA flatly re­fused to cer­tify it be­cause the undu­pli­cated drive train was deemed in­ad­e­quate. But that con­fig­u­ra­tion, un­ac­cept­able to the FAA in a fixed-wing, is an in­escapable fact of life in twin-en­gined he­li­copters.

The reg­u­la­tory ob­ses­sion with en­gine fail­ure causes ac­ci­dents. Un­der Group A En­gine Fail­ure Ac­count­abil­ity Pro­ce­dures, a com­mer­cial twin climbs back­wards to a given height so that in case of en­gine fail­ure it can land back where it took off. (Twins can­not re­main air­borne on one en­gine at all regimes of flight.) But quite apart from the risks of fly­ing up­wards and back­wards into an area the pi­lot can­not see, the pi­lot finds him­self at the top of the ini­tial climb with lit­tle or no air­speed, and pulling enor­mous torque. If tail ro­tor thrust gives out at that point (sta­tis­ti­cally more likely than en­gine fail­ure, at a con­ser­va­tive one per 50,000 hours) the air­craft will be­gin to spin and the pi­lot will have in­suf­fi­cient height to re­cover, what­ever his skill level. On the other hand, if a sin­gle-en­gined he­li­copter takes off on a nor­mal pro­file, seek­ing to gain air­speed as quickly as pos­si­ble, and suf­fers a tail ro­tor fail­ure at the point at which the twin would be at the top of its back­wards climb, the sin­gle can fly on to a safe land­ing.

If you study the nine­teen fa­tal ac­ci­dents in the last ten years, you’ll find all sorts of causes not re­lated to en­gines: tail ro­tor fail­ure, mid-air col­li­sion, loss of con­trol in IMC or at night, train­ing ac­ci­dents, col­li­sion with a crane, CFIT, carb ic­ing, low ro­tor RPM. The only in­stance of en­gine fail­ure was a 36-year-old Je­tranger that crashed at Flam­bor­ough Head in 2014, killing two. The es­tab­lish­ment of RMT 0318 shows us that EASA un­der­stands the is­sue, but ICAO’S in­ter­ven­tion proves that the quasi-religious at­tach­ment to en­gine fail­ure is too deeply in­grained in those who mat­ter.

There are dozens of rea­sons why sin­gles are bet­ter. A sin­gle au­toro­tates at about 20mph ver­ti­cally, so even if the pi­lot ut­terly ne­glects to flare off de­scent rate, it will ar­rive like a small fam­ily car run­ning into a lamp post at a brisk cy­cling speed. The very com­plex­ity of twins dou­bles the chance of com­po­nent fail­ure−the Glas­gow EC135 had six fuel pumps, enough fuel on board to con­tinue flight and a highly ex­pe­ri­enced pi­lot, but the com­plex­ity did them in: re­duc­ing com­plex­ity in­creases safety. Sin­gles have a greater power mar­gin, as twins op­er­ate two en­gines at low power on the ba­sis that they’ll need to scream one en­gine up to max torque if the other fails; sin­gles will also have greater tail ro­tor author­ity. Pay­loads on twins are of­ten lower be­cause of the need to carry the dead weight of a re­dun­dant en­gine and all its sys­tems, so they may have to make two trips where a sin­gle would fly one, and that ut­terly de­stroys any safety ar­gu­ment. Cost, noise, pol­lu­tion, down­wash, all count against the twin. Du­pli­ca­tion has its lim­its: the EC225 that got into vor­tex ring at Sum­burgh had du­pli­cate pi­lots, both highly ex­pe­ri­enced. Re­li­a­bil­ity is more im­por­tant than re­dun­dancy, and what nur­tures re­li­a­bil­ity is sim­plic­ity.

The ‘stands to rea­son’ brigade and their religious fix­a­tion should not be al­lowed to trump facts, statistics and science to the detri­ment of the he­li­copter world. It is whis­pered, how­ever, that the loud­est voice at ICAO for man­dat­ing two en­gines for com­mer­cial work em­anates from the UK. Please god, make it not so.

The rules on twins are based on an en­tirely false 'safety' premise

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