Safety Mat­ters

Safety Mat­ters and Safety Briefs are based on the AAIB Bul­letin, with additional ma­te­rial from the US Na­tional Trans­porta­tion Safety Board

Pilot - - CONTENTS -

Pi­o­neer fa­tal­ity, Mer­lin mal­func­tion, and more on air dis­plays

Tech­ni­cal fault, weather & high work­load

Air­craft Type: Alpi Pi­o­neer 400T Date & Time: 3 Jan­uary 2015 at 1528 Com­man­der’s Fly­ing Ex­pe­ri­ence: PPL, 201 hours, 5 on type) Last 90 days: 7 hours Last 28 days: 2 hours Af­ter an overnight stay on the Isle of Wight, the pi­lot and his wife and son were re­turn­ing from Bem­bridge Air­port to the air­craft’s base near Eve­sham. The weather was over­cast and misty so the pi­lot made ar­range­ments to stay a sec­ond night if nec­es­sary but later, when he judged that there was suf­fi­cient im­prove­ment in the weather, he took off from the un­manned air­field at 1500. A re­tired mil­i­tary pi­lot saw the air­craft take off. He lost sight of it due to poor vis­i­bil­ity when it was about two miles away from him, when he es­ti­mated the cloud base at no higher than 1,000ft agl, and when rain be­gan to fall thirty min­utes later it re­duced to an es­ti­mated 300ft/ half-a-mile.

In Popham’s club­house several peo­ple heard the sound of an air­craft whose height was es­ti­mated at 150-400ft agl, just be­low the cloud­base. One pi­lot, who was also a qual­i­fied tech­ni­cian on Ro­tax en­gines, one of which pow­ered the Pi­o­neer, re­marked that the engine sounded as if it had a prob­lem. A wit­nesses who watched the air­craft as it was close to Popham’s western boundary saw it turn left and cross the A303 road which par­al­lels the air­field at an es­ti­mated 70-80kt and 200ft agl, ap­par­ently on a left base leg for Rwy 03 but ‘too low’. He was sur­prised when the engine seemed to be throt­tled back and be­come qui­eter while the air­craft de­scended gen­tly. Other wit­nesses saw it de­scend­ing east­wards and pass through the ex­tended cen­tre­line of Rwy 03 un­til it was hid­den from view by trees. A pass­ing mo­torist re­ported that its wings were ‘wob­bling’ and its nose was ‘go­ing down and up’. When he lost sight of it he called the po­lice, as did Popham’s ra­dio op­er­a­tor as he was con­cerned for the air­craft’s

safety af­ter it dis­ap­peared from view. An air am­bu­lance he­li­copter quickly lo­cated the Pi­o­neer’s wreck­age in wood­land about a quar­ter of a mile south-east of the air­field. The pi­lot and his wife had suf­fered fa­tal in­juries. Their son, who was in the right front seat and se­ri­ously in­jured, was ex­tracted from the in­verted fuse­lage nearly an hour af­ter the ac­ci­dent when the fire ser­vice ar­rived. He later said that he had been told to brace for im­pact but was un­able to re­call any­thing else about the flight.

De­tailed ex­am­i­na­tion of the air­craft and its sys­tems by the AAIB re­vealed chaf­ing dam­age to the throt­tle po­si­tion sen­sor wire in the wiring loom that was not con­sis­tent with im­pact dam­age. ‘The dam­age to the wire from the throt­tle po­si­tion sen­sor to the turbo con­trol unit (TCU) would have cre­ated a ground on the wire, caus­ing the TCU to drive the waste­gate of the turbo fully closed and trig­ger an or­ange flash­ing TCU warn­ing light on the in­stru­ment panel,’ says the AAIB re­port. ‘It is also likely that engine man­i­fold pres­sure and rpm would have in­creased in re­sponse to the turbo be­com­ing ac­tive, al­though with the throt­tle be­low the take­off power po­si­tion, it is un­likely the engine would have ex­ceeded any oper­at­ing lim­i­ta­tions at this point.

‘Given a warn­ing no­tice con­tained in the engine’s Op­er­a­tor’s Man­ual [and the pi­lot’s] fa­mil­iari­sa­tion train­ing [in the air­craft], it is likely that his re­sponse was to iso­late the elec­tri­cal power to the TCU by pulling the cir­cuit breaker. This would have frozen the servo valve and thus the turbo waste­gate in the fully closed po­si­tion. It would also have pre­vented the over­speed pro­tec­tion logic and the or­ange and red warn­ing lights from work­ing… [Thus] the pi­lot may have di­verted to Popham to min­imise the flight time with a turbo fault, or it may have been be­cause the weather was too poor to con­tinue. Popham was near the planned route, he had passed it on the [pre­vi­ous day’s] flight south, and he was likely to have had it dis­played on the nav­i­ga­tion app on his tablet com­puter. The sub­se­quent de­scent and track, recorded on radar, are con­sis­tent with this. The lack of any ra­dio call to Southamp­ton or to Popham, and the fact that the Popham fre­quency had not been se­lected, sug­gest the pi­lot was fully oc­cu­pied as he dealt with poor weather, a mal­func­tion­ing turbo and di­vert­ing to an un­fa­mil­iar air­field.

‘With the turbo waste­gate fully closed, the pi­lot would have had to limit the throt­tle po­si­tion to keep the engine pa­ram­e­ters within limits. With the TCU not pow­ered, the only additional warn­ing of an engine ex­cee­dence was the rpm dis­play on the Engine In­for­ma­tion Sys­tem turn­ing yel­low and then red. How­ever, this dis­play was very small and the pi­lot may have over­looked it when he was pre­par­ing to land at an un­fa­mil­iar air­field in poor weather. If he con­ducted a go-around from an ap­proach to Rwy 26, he man­aged to do so with­out caus­ing a cat­a­strophic engine ex­cee­dence. How­ever, dur­ing the sub­se­quent cir­cuit, when head­ing east the engine stopped and the air­craft stalled into trees.

‘It was not pos­si­ble to de­ter­mine whether the pi­lot in­ad­ver­tently se­lected too high a throt­tle po­si­tion, was un­aware of the po­ten­tial con­se­quences of de­pow­er­ing the TCU, or he had no al­ter­na­tive in or­der to try to main­tain air­speed and al­ti­tude. How­ever, with the TCU pro­tec­tion logic dis­abled, there was no limit on the man­i­fold pres­sure pro­duced by the turbo un­til it reached its max­i­mum per­for­mance. The engine man­u­fac­turer con­firmed that ex­ces­sive man­i­fold air pres­sure could re­sult in mis­align­ment of the engine crank­shaft to an ex­tent that the engine would seize. The ev­i­dence from the engine strip and the lo­ca­tion and lack of dam­age to the pro­pel­ler blades sup­port the con­clu­sion that the engine stopped in flight for this rea­son. One wit­ness no­ticed the engine noise re­duce be­fore the air­craft was lost from view. ‘Whilst a very spe­cific de­fect oc­curred on this air­craft, the engine was still ca­pa­ble of be­ing op­er­ated safely with an in­creased level of pi­lot mon­i­tor­ing and aware­ness. It most likely only stopped as a re­sult of the throt­tle be­ing moved by the pi­lot to a set­ting where a da­m­ag­ing level of man­i­fold pres­sure was reached. Re­gard­less of this, pi­lots with an SEP Class rat­ing are trained in the need to an­tic­i­pate engine fail­ures for any rea­son and to con­duct forced land­ings when nec­es­sary.

‘The pi­lot ap­par­ently warned the pas­sen­gers to brace, in­di­cat­ing that he was con­scious im­me­di­ately be­fore the ac­ci­dent and aware that the air­craft was about to crash. With no engine power avail­able, it is pos­si­ble that the pi­lot re­tracted any flap that had al­ready been ex­tended in an ef­fort to ex­tend the glide and clear the trees. Re­tract­ing the flap would have re­duced the drag but it would have in­creased the stall speed, and the ev­i­dence from the car driver sug­gests that the air­craft stalled be­fore it struck the trees.’

In re­gard to weather con­di­tions dur­ing the flight, the AAIB notes: ‘When the pi­lot reached the main­land coast it was likely that he saw a de­te­ri­o­ra­tion in the weather that eroded the safety mar­gins for VFR flight. At this early stage it would have been pru­dent to di­vert to a suit­able nearby air­field or to have turned back to Bem­bridge… The poor weather con­di­tions at Popham meant the pi­lot, who had limited fly­ing ex­pe­ri­ence, es­pe­cially on this air­craft type, had to fly be­low the nor­mal cir­cuit height. This would have in­creased his work­load and re­duced the time avail­able in which to make crit­i­cal de­ci­sions. When com­bined with the additional work­load cre­ated by the engine fault, this may have led to the cir­cum­stances sur­round­ing the fail­ure of the engine and would then have limited the op­tions avail­able when con­fronted with the need to per­form a forced land­ing.’

As a re­sult of this ac­ci­dent the AAIB has made rec­om­men­da­tions to the air­craft’s air­frame and engine man­u­fac­tur­ers re­gard­ing the func­tions of engine and TCU warn­ing lights and ap­pro­pri­ate ac­tions to be taken, and the de­sign of Ro­tax 914 wiring looms. The Light Avi­a­tion As­so­ci­a­tion, un­der whose aus­pices the air­craft was op­er­ated, is con­duct­ing re­views of dif­fer­ences train­ing re­quire­ments for pi­lots oper­at­ing air­craft with tur­bocharged en­gines, and also the min­i­mum re­quire­ments for in­stru­men­ta­tion and waste­gate con­trol sys­tems for this type of engine.

Mer­lin mis­for­tune

Air­craft Type: Spit­fire IX Date & Time: 1 Au­gust 2015 at 1300 Com­man­der’s Fly­ing Ex­pe­ri­ence: ATPL, 7,710 hours, 294 on type Last 90 days: 145 hours Last 28 days: 52 hours Af­ter take­off from Rwy 29 at Big­gin Hill the pi­lot re­tracted the un­der­car­riage and re­duced power to 2,400rpm and +4 boost but, one or two sec­onds later, he heard the engine ‘cough’, so he turned the air­craft back to­wards the air­field, in­tend­ing to climb over­head to in­ves­ti­gate be­fore pro­ceed­ing. A few sec­onds later the engine lost power and the pi­lot could see flames com­ing from the right-hand ex­haust pipes.

He had only about ten to twenty per cent power, just suf­fi­cient to reach the air­field, but not to reach a run­way, so as the boundary was crossed the pi­lot lev­elled the wings and landed straight ahead, fear­ing that oth­er­wise the air­craft might stall. The Spit­fire touched down on its main wheels on waste ground and was head­ing to­wards a line of trees. The pi­lot tried to steer to­wards a small gap between them but the right wing struck a tree and de­tached. The air­craft spun round and ran back­wards up a bank be­fore com­ing to rest on its right side. The pi­lot suf­fered only mi­nor in­juries.

A limited ex­am­i­na­tion of the engine af­ter the ac­ci­dent sug­gested that a cylin­der in the right bank had a bro­ken in­let valve spring with a pen­e­tra­tion of the as­so­ci­ated in­duc­tion flame trap. It is un­clear whether this alone would have ac­counted for the sub­stan­tial power loss.

Air­shows need more risk as­sess­ment and CAA over­sight

The AAIB has pub­lished a third Spe­cial Bul­letin con­cern­ing its on­go­ing in­ves­ti­ga­tion into the Hawker Hunter ac­ci­dent dur­ing last year’s Shore­ham Air­show. Whilst still not its fi­nal re­port, the Bul­letin makes four­teen safety rec­om­men­da­tions that are broadly in line with new CAA rules aris­ing from the Author­ity’s own review of air dis­play safety. The AAIB’S rec­om­men­da­tions fall into four main cat­e­gories:

1 Risk man­age­ment

The AAIB asked the in­de­pen­dent Health and Safety Lab­o­ra­tory to review the risk as­sess­ment car­ried by the or­gan­is­ers of the Shore­ham Air­show. ( Note that the Shore­ham Fly­ing Dis­play Di­rec­tor was a dis­play pi­lot and Dis­play Au­tho­ri­sa­tion Ex­am­iner (DAE) and was for­merly the CAA’S head of GA — and the air­show or­gan­is­ers did carry out a risk as­sess­ment, de­spite re­cent me­dia re­ports to the con­trary — Ed). The five rec­om­men­da­tions to the CAA un­der this head­ing cover pro­duc­ing im­proved guid­ance to en­able or­gan­is­ers to man­age risks and how they con­duct risk assess­ments; the safety man­age­ment and other com­pe­ten­cies a fly­ing dis­play or­gan­iser should demon­strate; what in­for­ma­tion dis­play air­craft com­man­ders must pro­vide to the or­gan­iser re­gard­ing their in­tended se­quence of ma­noeu­vres and the area over which they in­tend to per­form them; and, for Per­mit to Fly air­craft, ev­i­dence that the ma­noeu­vres con­form with the air­craft’s Per­mit lim­i­ta­tions.

2 Min­i­mum heights

A pi­lot’s Dis­play Au­tho­ri­sa­tion (DA) gives a min­i­mum height at which the holder may fly dur­ing a dis­play with an as­sump­tion that ‘nor­mal rules of the air’ ap­ply away from the dis­play line. As this gives rise to a po­ten­tial lack of clar­ity, the AAIB rec­om­mends that the CAA re­move the gen­eral ex­emp­tion to flight at min­i­mum height and spec­ify the bound­aries of a fly­ing dis­play within which any per­mis­sion ap­plies.

3 Sep­a­ra­tion dis­tances

Air dis­play sep­a­ra­tion dis­tances between dis­play lines and spec­ta­tor en­clo­sures have re­mained un­changed for several years and, in gen­eral, the CAA’S man­dated dis­tances re­main less than those of the US Fed­eral Avi­a­tion Ad­min­is­tra­tion and other coun­tries’ avi­a­tion au­thor­i­ties. The AAIB makes three rec­om­men­da­tions: that the CAA re­quire dis­play­ing air­craft be sep­a­rated from the pub­lic by a dis­tance suf­fi­cient that the risk of in­jury in case of an ac­ci­dent is min­imised; spec­ify the min­i­mum sep­a­ra­tion dis­tances between dis­play air­craft and ‘sec­ondary crowd’ (i.e. non-pay­ing spec­ta­tor) ar­eas; and re­quire or­gan­is­ers to des­ig­nate airspace for aer­o­bat­ics and safe­guard the peo­ple and struc­tures be­low that space.

4 Pi­lot stan­dards

The AAIB found that dis­play pi­lots, in­clud­ing the Shore­ham Hunter pi­lot, have been eval­u­ated by DAES who were mem­bers of the same team or al­ready known to them. Pi­lots have also been able to re­new their DAS on one type while in­tend­ing to dis­play several classes or types of air­craft, and there has been no reporting re­quire­ment for oc­cur­rences where it is felt nec­es­sary to stop a pi­lot’s dis­play on safety grounds. The AAIB rec­om­mends that DAES have no con­flict of in­ter­est with can­di­dates and that a DA is re­newed for each class or type or air­craft the holder in­tends to fly. Ad­di­tion­ally, the CAA should pub­lish a list of oc­cur­rences and in­sti­tute a process to sus­pend the DA of any pi­lot whose com­pe­tence is in doubt.

In terms of safety stan­dards, the AAIB noted that CAA ex­perts at­tend less than ten per cent of dis­plays for which the Author­ity has given per­mis­sion, whereas rep­re­sen­ta­tives of the FAA at­tend ev­ery au­tho­rised dis­play. The AAIB rec­om­mends that the CAA should es­tab­lish and pub­lish tar­get safety in­di­ca­tors for dis­play fly­ing. The full bul­letin is at: gov.uk/aaib-re­ports

Alpi Pi­o­neer 400T: Dave Un­win flight tested the first UK ex­am­ple of this type for the Novem­ber 2011 edi­tion of Pi­lot

In its lat­est Spe­cial Bul­letin, the AAIB makes four­teen safety rec­om­men­da­tions that will im­pact all dis­play fly­ing and not just fast jets

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