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


Tiger tragedy

Air­craft Type: DH Tiger Moth Date & Time: 26 Au­gust 2017 at 0828 Com­man­der’s Fly­ing

Ex­pe­ri­ence: PPL (for­mer RAF pi­lot and ATPL), 22,240 hours, 512 on type Last 90 days: 50 hours Last 28 days: 24 hours The Comp­ton Ab­bas-based air­craft was mak­ing its first flight of the day, a thirty-minute in­tro­duc­tory trip for the pas­sen­ger, who had no fly­ing ex­pe­ri­ence. Take­off was from Rwy 08 and wit­nesses saw the Tiger Moth be­come air­borne at about the 300m marker, at which point its en­gine was heard to mis­fire, but the air­craft con­tin­ued to climb. The air­field does not record trans­mis­sions on its A/G fre­quency, but the op­er­a­tor heard the pi­lot trans­mit in an ap­par­ently calm voice that he had a “rough run­ning en­gine” and was mak­ing a 180° turn to land back on Rwy 26. Dur­ing the turn, or when rolling out of it, the air­craft ap­peared to slow and be­come un­sta­ble be­fore a wing dropped sharply and it de­scended rapidly in a turn which a wit­ness thought was to the right. An­other wit­ness heard and then saw the air­craft climb­ing slowly at low air­speed, with the en­gine “sound­ing aw­ful and mis­fir­ing” be­fore it de­scended, “corkscrew­ing down”.

A fly­ing in­struc­tor who was next to the ra­dio op­er­a­tor when he heard the trans­mis­sion in­di­cat­ing en­gine trou­ble saw the air­craft head­ing north some 1-2nm from the air­field at a height of about 500ft, then make a gen­tle, de­scend­ing left turn onto right base leg for Rwy 26. When it was at about twice the height of trees at the eastern end of the air­field, and some 200m be­yond them, its nose pitched sharply down and it rolled to the left in a steep de­scend­ing turn. Shortly after­wards a col­umn of smoke was seen.

The Tiger Moth had crashed in a corn­field in a steep nose­down at­ti­tude. Post-crash fire con­sumed most of its fab­ric cov­er­ing and cock­pit struc­ture, in­clud­ing the seats, both safety har­nesses, in­stru­ments, in­stru­ment pan­els and elec­tri­cal wiring. A pathol­o­gist sub­se­quently con­cluded that the im­pact in­juries sus­tained by both oc­cu­pants prior to the fire had not been sur­viv­able. AAIB ex­am­i­na­tion of the wreck­age showed that the fly­ing con­trols had been con­nected prior to the ac­ci­dent, but it was not pos­si­ble to de­ter­mine their po­si­tions at im­pact. The en­gine had suf­fered im­pact and fire dam­age, but there was no ev­i­dence of me­chan­i­cal fail­ure prior to the ac­ci­dent.

As part of the in­ves­ti­ga­tion two trial flights with Tiger Moths were made to es­tab­lish take­off, climb and de­scent per­for­mance at dif­fer­ent air­speeds, at full power and with the throt­tle closed, and with vary­ing an­gles of bank in the turns. From this data height gained or lost against time and/ or dis­tance could be cal­cu­lated. It was not pos­si­ble to de­ter­mine the ef­fects, if any, of the pi­lot’s re­port of a “rough run­ning en­gine” on the per­for­mance of the ac­ci­dent air­craft, but rates of climb recorded in the tri­als were greater than those es­ti­mated for the ac­ci­dent flight. The fi­nal two test points sim­u­lated turn­back ma­noeu­vres as­sum­ing a worst case in which the power avail­able from the en­gine was equiv­a­lent to idle. The test pi­lot climbed to 800ft and closed the throt­tle, low­ered the nose to achieve a tar­get speed of 66mph, and rolled the air­craft to a 45° an­gle of bank to start a sim­u­lated turn back to the air­field.

He found that both the Tiger Moths flown had sim­i­larly be­nign stall char­ac­ter­is­tics at be­tween 45-49mph IAS, adopt­ing a high an­gle of at­tack and rate of de­scent with the stick held fully back, and showed no ten­dency to drop a wing. The mea­sured rates of de­scent were con­sis­tent with other Tiger Moths he had flown, but with a no­tice­able in­crease when flown at or just above stall speed. The air­craft could be turned rel­a­tively eas­ily with an in­creas­ing rate of turn, ap­prox­i­mately 45° bank be­ing the op­ti­mum for a turn back to­wards an air­field. Height loss in turns through 180° was ap­prox­i­mately 400ft. The test pi­lot con­sid­ered that start­ing such a ma­noeu­vre much be­low 800ft, fol­low­ing a to­tal en­gine fail­ure, would have given the pi­lot lit­tle op­por­tu­nity to ma­noeu­vre onto the re­cip­ro­cal run­way.

A third trial was flown to as­sess re­jected take­off per­for­mance, climb per­for­mance at par­tial power/ low rpm, and air­craft at­ti­tude in a glide at min­i­mum rate of de­scent. The test pi­lot re­ported: “Re­ject­ing the take­off in the Tiger Moth in­tro­duced a num­ber of chal­lenges. The air­craft was not fit­ted with wheel brakes, had a very crude steer­able rear tail­skid and was a ‘tail­drag­ger’ con­fig­u­ra­tion. Re­ject­ing the take­off when the wheels were still in con­tact with the run­way re­quired the throt­tle to be closed and the level at­ti­tude held ini­tially be­fore al­low­ing the tail to drop gen­tly as the air­speed re­duced. Dur­ing this pe­riod there was no brak­ing, and steer­ing was en­tirely aero­dy­namic and re­liant on air­flow over the rud­der (which was re­duced with loss of pro­pel­ler wash). This tech­nique worked sat­is­fac­to­rily and, from be­ing light on the wheels at 40KIAS, the air­craft was brought to a halt in ap­prox­i­mately 230m after clos­ing the throt­tle and fol­low­ing an ini­tial take­off run of 200m.

'The sit­u­a­tion be­came slightly more prob­lem­atic once the air­craft had be­come fully air­borne. Typ­i­cally, the air­craft would be landed in a "three­p­oint" at­ti­tude, main wheel and tail­skid con­tact­ing the run­way at the same time in a stalled or semi-stalled con­di­tion with min­i­mum ground and air­speeds. Re­ject­ing the take­off once air­borne at 40+kt IAS meant that the ini­tial ap­pli­ca­tion of aft con­trol stick would have po­ten­tially caused the air­craft to climb be­fore the "three-point" land­ing at­ti­tude was reached, which would have re­sulted in a heavy land­ing. The al­ter­na­tive was to re­tain the level at­ti­tude and close the throt­tle, al­low­ing the air­craft to de­scend back onto the run­way ini­tially on the main­wheels and then com­plete the re­ject. Any de­lay in mak­ing the de­ci­sion to re­ject once air­borne would no­tice­ably ex­tend the dis­tance re­quired to com­plete the ma­noeu­vre [and] given the risks of per­form­ing such a ma­noeu­vre once air­borne it is un­likely that it was prac­tised reg­u­larly, if at all. This type of re­ject was at­tempted dur­ing the sor­tie when the air­craft had reached about 20ft agl and a fly­ing speed of 50kt IAS. As the throt­tle was closed and the nose dropped to a level at­ti­tude for land­ing… in­suf­fi­cient run­way re­mained to com­plete the land­ing with­out risk, and power was re-ap­plied to climb away.'

The AAIB re­port con­cludes: ‘On take­off the en­gine was

heard to mis­fire, but the air­craft con­tin­ued to climb. It would have been pos­si­ble to aban­don the take­off, clos­ing the throt­tle and at­tempt­ing to stop on the run­way. If the de­ci­sion was made promptly there would have been suf­fi­cient space re­main­ing for the air­craft to stop or turn away from the ob­sta­cles at the eastern bound­ary. Once the air­craft was air­borne, the pi­lot would have faced the same sit­u­a­tion ob­served by the test pi­lot dur­ing sor­tie three of the flight trial. Dur­ing the ac­ci­dent take­off, en­gine speed re­duced to 1,710rpm. This may have been a re­sult of the pi­lot re­duc­ing throt­tle in or­der to re­ject the take­off. How­ever, the take­off con­tin­ued and he may have con­cluded that there was in­suf­fi­cient run­way or other space on the air­field in which to stop.

‘Flight tri­als in­di­cated that power set­tings 1,700 and 1,800 rpm would not have been suf­fi­cient to achieve the height gained in the time avail­able. Al­though the pi­lot had re­ported “rough run­ning”, the en­gine must have been pro­duc­ing suf­fi­cient power to achieve be­tween 1,900-2,000rpm at the best rate of climb speed in or­der to gain be­tween 300-500ft above air­field level in the time avail­able.

'Sub­se­quently, both the turn and de­scent back to­wards the air­field were gen­tle ma­noeu­vres, and there were no ad­di­tional trans­mis­sions from the pi­lot re­port­ing any de­te­ri­o­ra­tion in his sit­u­a­tion. Wit­ness ev­i­dence var­ied re­gard­ing the flight path, dis­tance from the air­field and the di­rec­tion of the turn back to­wards it… Up to this point, the gen­tle rate of de­scent sug­gests that the en­gine was still pro­duc­ing power but was not, and prob­a­bly could not be, heard from out­side the fly­ing club if at re­duced power. The pi­lot ei­ther made a nor­mal ap­proach, throt­tling back and de­scend­ing on base leg or, if power avail­able had re­duced and he was un­able to main­tain height, was forced to let the air­craft de­scend. With a rough run­ning en­gine… a to­tal or in­creased loss of power is al­ways a pos­si­bil­ity, and main­tain­ing height un­til within glid­ing dis­tance of the in­tended land­ing point is de­sir­able in this sit­u­a­tion if it can be achieved whilst main­tain­ing suf­fi­cient speed.

‘The air­craft’s nose was seen to pitch pos­i­tively down some 30°, which when com­bined with the turn, would have caused the air­craft to lose height rapidly. Flight tri­als es­tab­lished that the rate of de­scent could have been at least 1,200ft/min if the air­craft was just above the stall at low speed and low power.

‘Three pos­si­ble rea­sons for the fi­nal ma­noeu­vre were con­sid­ered: (1) Low air­speed re­sult­ing from try­ing to main­tain height which caused a wing to drop at the stall, as de­scribed by one wit­ness; (2) Low air­speed re­sult­ing in the need for a large nose-down at­ti­tude change in or­der to re­gain air­speed but re­sult­ing in a sig­nif­i­cant rate of de­scent; or (3) A late de­ci­sion to change the land­ing area to the crop field, re­quir­ing a tight left turn. This would have re­quired an in­crease in air­speed, ob­tained by the sig­nif­i­cant nose-down at­ti­tude change be­fore the turn. Ei­ther (1) or (2) may have caused the air­craft to de­scend be­low the min­i­mum glide an­gle re­quired to land at the air­field. In these cases, the pi­lot may have recog­nised that he was not able to re­turn to the air­field and turned to­wards the large open area of crop field. Al­ter­na­tively, the an­gle of the de­scent placed the air­craft at a height and po­si­tion from which the pi­lot de­cided to change his land­ing area to the crop field. He may also have been at­tempt­ing to re­cover from or avoid a loss of con­trol at low air­speed.

‘Dam­age sus­tained dur­ing the ac­ci­dent pre­vented an as­sess­ment of the mag­ne­tos, ig­ni­tion sys­tem and car­bu­ret­tor. A prob­lem with any one of these could have caused the re­ported symp­toms. The pos­si­bil­ity of car­bu­ret­tor ic­ing could not be dis­counted. Fi­nally, there was ei­ther in­suf­fi­cient height to re­cover, or a re­stric­tion of the con­trols that pre­vented re­cov­ery be­fore im­pact. The ac­ci­dent air­craft was fit­ted with dual con­trols and al­though the pas­sen­ger had re­ceived a full cock­pit and safety brief, it is pos­si­ble the fly­ing con­trols were in­vol­un­tar­ily re­stricted as the pas­sen­ger re­acted to what would have been a very stress­ful sit­u­a­tion.’

Sea­side slipup

Air­craft Type: Piper Chero­kee Archer II Date & Time: 13 June 2018 at 1148 Com­man­der’s Fly­ing Ex­pe­ri­ence: PPL, 387 hours, 347 on type Last 90 days: 7 hours Last 28 days: 1 hour The pi­lot had planned to fly to Skeg­ness for a day trip with a friend. He tele­phoned the air­field for PPR and was told that A/G ra­dio was not op­er­at­ing that day, but hav­ing been there be­fore he de­cided to make the flight, in­tend­ing to land on the 799m Rwy 03/21, the longer of the air­field’s two grass strips. On ar­rival the pi­lot saw no wind­sock and, de­spite mak­ing two level cir­cuits at 1,000ft, nei­ther oc­cu­pant could see the run­way’s ground mark­ings, so he de­cided to use the shorter, 650m 11/29 strip, which he could see.

He flew a left-hand cir­cuit for Rwy 11 at 1,000ft and turned fi­nal at 700ft, but to­wards the end of the ap­proach re­alised that he was go­ing to land far down the run­way so he went around. As he did so the air­craft clipped a hedge be­yond the de­par­ture end of the run­way, and some fo­liage be­came at­tached to the air­frame. The pi­lot strug­gled to main­tain con­trol and pre­vent the air­craft from stalling, turned right “with dif­fi­culty” to avoid a car­a­van park ahead and flew a non­stan­dard right hand cir­cuit over clear ground. He stated that the air­craft would only re­main air­borne with full power se­lected, and while rud­der and el­e­va­tor ap­peared to re­spond nor­mally, the ailerons were op­er­at­ing “strangely”. Due to the high power set­ting, the Archer touched down at around 90kt. Brak­ing had lit­tle ef­fect, and as it neared the end of the run­way the pi­lot shut down the en­gine and told the pas­sen­ger to brace, then slewed the air­craft to the right so as to avoid some trees si­t­u­ated within the same hedge that had been struck on the first land­ing at­tempt. The Archer came to rest in the hedge, which blocked its doors and pre­vented pi­lot and

pas­sen­ger from es­cap­ing un­til res­cuers ar­rived about fif­teen min­utes later.

The pi­lot re­flected that his choice of run­way was a fac­tor in the ac­ci­dent, and that the winds ap­peared to be more west­erly than he had orig­i­nally thought. Prior to the flight, he had checked run­way in­for­ma­tion on the Skeg­ness Air­field web­site, which de­scribes them as: ‘Run­ways 03/21 799m x 23m, 11/29 650m x 23m. All cir­cuits in­land: 03/11 LH, 21/29 RH’.

Notes the AAIB: ‘The de­scrip­tion of the run­ways and the cir­cuit di­rec­tions may have con­trib­uted to some con­fu­sion by the pi­lot over the run­way des­ig­na­tions. Since the ac­ci­dent Skeg­ness Air­field stated that it in­tends to al­ter its web­site to em­pha­sise the run­way des­ig­na­tions.’

Lat­est Air­proxes

At its De­cem­ber meet­ing the UK Air­prox Board re­viewed 29 in­ci­dents, nine­teen of which in­volved drones/uass. Among the air­craft-to-air­craft in­ci­dents, four had a def­i­nite risk of col­li­sion (three Cat­e­gory A ‘with prov­i­dence play­ing a ma­jor part’, and one Cat­e­gory B where ‘safety was much re­duced as a re­sult of serendip­ity, mis­judge­ment, in­ac­tion, or late sight­ing’).

Up to the De­cem­ber meet­ing, at 181 the over­all num­ber of air­craft-to-air­craft in­ci­dents in 2018 was just above the ex­pected five-year an­nual av­er­age. In con­trast, there were 132 re­ported drone/suas in­ci­dents, well in ex­cess of the 113 recorded in 2017.

‘Pre­dom­i­nant themes were poor look­out and non-/late­sight­ings which… ac­counted for six in­ci­dents,’ says the Board. ‘Given that most in­ci­dents oc­curred in see-and-avoid Class G airspace this isn’t per­haps sur­pris­ing. How­ever, in at least two in­ci­dents the Board felt the sub­ject pi­lots should have been do­ing more to en­hance their chances of see­ing the other air­craft by pay­ing more at­ten­tion to look­out.

That said, the va­garies of the human eye in the avi­a­tion en­vi­ron­ment were ac­knowl­edged.

‘In­ac­tion fea­tured in three in­ci­dents where pi­lots could have done more when be­com­ing aware of the other air­craft. One was par­tic­u­larly dis­ap­point­ing when a pi­lot didn’t give way be­cause he thought he would carry on rather than cause his stu­dent prob­lems by de­vi­at­ing from his stu­dent’s navex track.’ The Board em­pha­sised that ‘avoid­ing’ doesn’t nec­es­sar­ily have to be in just the hor­i­zon­tal plane – climb­ing or de­scend­ing would have been an op­tion in this case if it was im­por­tant not to over­load the stu­dent by turn­ing off track.

The re­main­ing in­ci­dents showed no clear trends ex­cept ‘where pi­lots could have helped them­selves by seek­ing a more ap­pro­pri­ate air traf­fic ser­vice other than a Ba­sic Ser­vice (or no ATS)’, says the Board. We’ve talked many times be­fore about the value of a surveil­lance­based Traf­fic Ser­vice, but the mes­sage still ap­pears to fail to reg­is­ter with some who ei­ther an­tic­i­pate they will not get such a ser­vice, so don’t even ask, or who think that they will re­ceive Traf­fic In­for­ma­tion when un­der a Ba­sic Ser­vice (which they might, but which is not the in­ten­tion or ex­pec­ta­tion with that level of ATS).’

Anal­y­sis of 116 in­ci­dents last year as­sessed prior to the De­cem­ber meet­ing showed that ATC was not avail­able for 26% of them. ‘There’s not much we can do about that in the short-term,’ says the Board, [but] the strik­ing statis­tic is that ATC were not used to pro­vide Traf­fic In­for­ma­tion when it might have been avail­able in 31% of the in­ci­dents. Al­though this in­cludes times when a sur­veil­lance-based ser­vice was not avail­able, a good pro­por­tion of these lat­ter in­ci­dents in­clude ATC not even be­ing called up, or pi­lots ask­ing for only a Ba­sic Ser­vice when a Traf­fic Ser­vice could have been used.’

The Board’s ‘Air­prox of the Month’ in­volved a Piper PA-28 and a Chris­ten Ea­gle, both in­bound to White Waltham (il­lus­tra­tion above). Both were join­ing over­head at the stan­dard mod­i­fied over­head join height of 1,300ft par­al­lel with the run­way. ‘The faster Chris­ten Ea­gle came in be­hind the PA-28, but its pi­lot hadn’t as­sim­i­lated the Piper pi­lot’s calls as he joined ahead,’ says the Board’s re­port, ‘[and] the Piper’s pi­lot had heard the Ea­gle pi­lot’s join­ing call but, al­though aware there might be a con­flict that he would need to be cau­tious about, he was taken by sur­prise when the Chris­ten Ea­gle over­flew from be­hind, de­scend­ing and miss­ing him by only a few feet. The Ea­gle pi­lot didn’t see the Piper but, for­tu­nately, the PA28 pi­lot’s stu­dent had al­lowed their height to de­crease to 1,230ft by mis­take, other­wise the en­counter could have ended in disas­ter.

‘Al­though a missed ra­dio call is some­thing that hap­pens now and again, we all need to re­mem­ber dur­ing our pre-join­ing checks that missed calls or even other ra­dio-fail­ure join­ers are al­ways a pos­si­bil­ity that needs to be fac­tored in to your de­ci­sion-mak­ing process. As you ap­proach the “honey pot” of an air­field where ev­ery­one is likely to be fol­low­ing the same track or route­ing to the same point at the same height dur­ing the join, it’s vi­tal that look­out ef­forts are re­dou­bled for just such a rea­son.

‘Don’t let your­self be­come task­fo­cused on the pro­ce­dure it­self, es­pe­cially if you’re in an air­craft with re­stricted views ahead such as the Chris­ten Ea­gle.

‘Along­side mak­ing all the right calls in the right place and fol­low­ing the pre­scribed route, weav­ing the nose, drop­ping a wing to mit­i­gate blind-spots, and metic­u­lous at­ten­tion to clear­ing your path ahead, above and be­low, are all es­sen­tial el­e­ments of any air­field join.’

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