Safety Mat­ters

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

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The Hunter tragedy at Shoreham in 2015 and other in­ci­dents

The Shoreham Hunter ac­ci­dent

The Air Ac­ci­dent In­ves­ti­ga­tion Branch’s fi­nal re­port into the crash of a Hawker Hunter T Mk.7 dur­ing the Shoreham Air Dis­play on 22 Au­gust 2015 was pub­lished on 3 March 2017. The fol­low­ing is a nec­es­sar­ily brief syn­op­sis of its 452-page find­ings, which can be downloaded in full at: gov.uk/aaib-re­ports

Af­ter hold­ing off­shore for his dis­play to start and briefly fly­ing in­verted, prob­a­bly to check for loose ar­ti­cles in the cock­pit, the pi­lot rolled up­right and wings level, de­scended to 800ft and made a right turn to line up with the dis­play line to the west of Shoreham’s Rwy 02/20. The Hunter re­mained right wing low with the an­gle of bank de­creas­ing as it de­scended to 100ft and flew along the dis­play line. It then started a gen­tle climb­ing right turn, ex­e­cuted a ‘Derry Turn’ to the left, which peaked at 1,800ft, then en­tered a de­scend­ing left turn to ap­prox­i­mately 185ft agl, ap­proach­ing the dis­play line at an an­gle of about 25°.

The Hunter then pitched up into the ac­ci­dent ma­noeu­vre at an in­di­cated air­speed of ap­prox­i­mately 310kt and with an en­gine speed of ap­prox­i­mately 7,500rpm. As it ap­proached the ver­ti­cal, the pi­lot ini­ti­ated a roll to the left. In the climb the en­gine speed first re­duced, then in­creased to about 7,200rpm, then re­duced again near­ing the apex. The air­craft was al­most in­verted with its wings level at the apex, at a height of ap­prox­i­mately 2,700ft. Dur­ing the sub­se­quent de­scent, its ground track was aligned to the west along the A27 Shoreham By­pass. As it de­scended it ac­cel­er­ated and the nose was raised, but in­suf­fi­cient height was avail­able to re­cover to level flight be­fore it con­tacted the west­bound car­riage­way. Eleven peo­ple died in ve­hi­cles on the road, and thir­teeen, in­cluded the pi­lot, were in­jured.

Dur­ing 2015 the pi­lot had flown one dis­play prac­tice and five dis­plays in the Hunter, the most re­cent four­teen days be­fore the ac­ci­dent. Both his cur­rency and the re­newal of his Dis­play Au­tho­ri­sa­tion, com­pleted in a Jet Provost and sub­se­quently RV-8 air­craft, com­plied with the reg­u­la­tions then in force.

The air­craft’s Rolls-royce Avon en­gine was sub­ject to a Manda­tory Per­mit Di­rec­tive (MPD) which im­posed a cal­en­dar life on the en­gine type, and pro­vided an op­tion to ex­tend that life us­ing an Al­ter­na­tive Means of Com­pli­ance (AMOC). Pro­pos­als for an en­gine life ex­ten­sion us­ing an AMOC in­spec­tion pro­gramme had to be ap­proved by the reg­u­la­tor. Re­lated tasks were be­ing con­ducted by the main­te­nance or­gan­i­sa­tion, but the reg­u­la­tor had not ap­proved either the op­er­a­tor or its main­te­nance or­gan­i­sa­tion to use an AMOC to this MPD.

On the tech­ni­cal front, AAIB in­ves­ti­ga­tors found that de­fects and exce­dences of the air­craft’s op­er­a­tional lim­its had not been re­ported to the main­te­nance or­gan­i­sa­tion, and manda­tory re­quire­ments of its Air­wor­thi­ness Ap­proval Note had not been met. Dur­ing pro­longed pe­ri­ods of in­ac­tiv­ity the air­craft’s Rolls-royce Avon en­gine had not been pre­served in ac­cor­dance with the ap­proved main­te­nance sched­ule. The in­ves­ti­ga­tion iden­ti­fied a de­graded di­aphragm in the en­gine fuel con­trol sys­tem, which could no longer be con­sid­ered air­wor­thy. How­ever, the en­gine man­u­fac­turer con­cluded that this would not have af­fected its nor­mal op­er­a­tion. The AAIB notes that in RAF ser­vice there had been sev­eral cases in­volv­ing the Rolls-royce Avon Mk 122, where en­gine speed had dropped and the sub­se­quent engi­neer­ing in­ves­ti­ga­tion had not es­tab­lished a clear cause.

The Hunter had been is­sued with a Per­mit to Fly and its Cer­tifi­cate of Va­lid­ity was in date, but the tech­ni­cal is­sues iden­ti­fied in the in­ves­ti­ga­tion in­di­cated that the air­craft was no longer in com­pli­ance with the re­quire­ments of its Per­mit.

A test pi­lot flew two data-gath­er­ing sor­ties in a sim­i­lar Hunter on 19 Oc­to­ber 2015 to­talling one hour, 25 min­utes. Fol­low­ing anal­y­sis from these sor­ties and other in­for­ma­tion gath­ered dur­ing the course of the in­ves­ti­ga­tion, a third, 55-minute sor­tie was flown on 4 De­cem­ber 2015. Based on the

data gath­ered dur­ing these sor­ties, the test pi­lot con­cluded that:

From the apex height and air­speed achieved in the ac­ci­dent ma­noeu­vre, and for up to at least four sec­onds af­ter pass­ing the apex, it would have been pos­si­ble for an ap­pro­pri­ately trained pi­lot to fly a straight­for­ward es­cape ma­noeu­vre, which would have pre­vented im­pact with the ground, by rolling the air­craft through 180° back to erect flight and then pulling out of the dive to re­gain level flight.

The mea­sured height loss dur­ing a rep­re­sen­ta­tive pull-through from the apex of a loop at the air­speed, all-up mass and den­sity alti­tude of the ac­ci­dent ma­noeu­vre was be­tween 2,700-2,850ft, and if al­time­ter read­ing res­o­lu­tion and in­stru­ment er­rors were con­sid­ered the range would in­crease to be­tween 2,600-2,950ft. The height loss ap­peared to be in­sen­si­tive to whether one or two notches of flap were se­lected and to the power set­ting.

The ‘bent’ loop tests in­di­cated that the apex height and air­speed of the ac­ci­dent ma­noeu­vre was con­sis­tent with a max­i­mum per­for­mance pull-up from 300 KIAS with sig­nif­i­cantly less than full thrust and with a 45-90° bend ini­ti­ated ap­prox­i­mately five sec­onds af­ter pull-up. They also showed that the apex height for a ‘bent’ loop was 300 to 400ft less than for a straight loop with all other pa­ram­e­ters con­stant.

A 90° ‘bent’ loop en­tered at 350 KIAS with full Hunter T Mk.7 thrust was, for an ap­pro­pri­ately trained pi­lot, a safe and straight­for­ward ma­noeu­vre to fly.

The test pi­lot also ob­served that any re­duc­tion in thrust was dif­fi­cult to de­tect and if the ac­ci­dent pi­lot had not throt­tled back in­ten­tion­ally he would prob­a­bly have been un­aware of it. In sum­mary, the AAIB con­cluded: The air­craft did not achieve suf­fi­cient height at the apex of the ac­ci­dent ma­noeu­vre to com­plete it be­fore im­pact­ing the ground be­cause the com­bi­na­tion of low en­try speed and low en­gine thrust in the up­ward half of the ma­noeu­vre was in­suf­fi­cient.

An es­cape ma­noeu­vre was not car­ried out, de­spite the air­craft not achiev­ing the re­quired min­i­mum apex height.

The fol­low­ing con­trib­u­tory fac­tors were also iden­ti­fied:

The pi­lot either did not per­ceive that an es­cape ma­noeu­vre was nec­es­sary, or did not re­alise that one was pos­si­ble at the speed achieved at the apex of the ma­noeu­vre.

The pi­lot had not re­ceived for­mal train­ing to es­cape from the ac­ci­dent ma­noeu­vre in a Hunter and had not had his com­pe­tence to do so as­sessed.

The pi­lot had not prac­tised the tech­nique for es­cap­ing from the ac­ci­dent ma­noeu­vre in a Hunter, and did not know the min­i­mum speed from which an es­cape ma­noeu­vre could be car­ried out suc­cess­fully.

A change of ground track dur­ing the ma­noeu­vre po­si­tioned the air­craft fur­ther east than planned, pro­duc­ing an exit track along the A27 dual car­riage­way.

The ma­noeu­vre took place above an area oc­cu­pied by the pub­lic over which the or­gan­is­ers of the fly­ing dis­play had no con­trol.

The sever­ity of the out­come was due to the ab­sence of pro­vi­sions to mit­i­gate the ef­fects of an air­craft crash­ing in an area out­side the con­trol of the or­gan­is­ers of the fly­ing dis­play.

See also the Bri­tish Air Dis­play As­so­ci­a­tion’s re­sponse to the AAIB re­port in ‘ Pi­lot Notes’, p.7.

Il­lus­tra­tion of the ac­ci­dent ma­noeu­vre, a ‘bent loop’. (This is an ap­prox­i­mate de­pic­tion of the air­craft’s be­hav­iour/flight­path)

A com­par­i­son of au­dio-de­ter­mined en­gine speed dur­ing loop­ing ma­noeu­vres flown by the same pi­lot dur­ing dif­fer­ent Hunter dis­plays (Ac­ci­dent ma­noeu­vre at top)

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