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the gremline digest — ignorance or overconfidence will kill you |
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Ignorance Will Kill You – Bolkow 207 “Ignorance of the law excuses no man: not that all men know the law, but because ’tis an excuse every man will plead, and no man can tell how to refute him.” John Selden 1584-1654
The history of fatal accidents to UK registered General Aviation aircraft is littered with examples of pilots who killed themselves and, too often, their passengers because they either did not understand the risks associated with their actions, or they decided to take the risk anyway. One can feel some sympathy for those who kill themselves through ignorance, but it is more difficult to feel sorry for those who apparently took a conscious decision to ignore the rules. I can only guess that those who decide to ignore the rules have done so previously and got away with it, and thus developed a contempt for all the rules and regulations related to flying.
This month’s Air Accidents Investigation Branch Bulletin (6/2008) contains no fewer than three Field Investigation reports that each involve pilots who either did not understand what they were doing wrong or else knew they were wrong and went ahead anyway. They all paid with their lives and, sadly, the lives of friends and family members.
The facts in the following report are based on AAIB Report EW/C2007/08/07 which source is gratefully acknowledged. Any comments or conclusions are those of the Gremline Technical Editor and do not seek to reflect the views of AAIB.
A Tragic Accident on Takeoff This tragic accident involved a 43 year old pilot who took his partner and their three-year-old daughter for a local pleasure flight from a private farm strip. The aircraft was a German registered single-engined tailwheel Bolkow 207 that the pilot had bought less than a year previously. He had undergone a five hour tailwheel conversion course on the Bolkow at an approved training organisation that operated from a level 800 metre paved runway. The conversion did not include short or soft-field takeoff techniques. The pilot did not ask for any advice on strip operations and the instructor assumed that the Bolkow was to continue to be operated from the paved runways at North Weald airport. The 03/21 farm grass strip is 680 metres long and drops about 10 metres towards the northern end. The aircraft was positioned at the southern end of the strip for a northerly takeoff. The adult female passenger was in the right front seat, the pilot in the left front seat and their three-year-old daughter in a car safety seat attached to the right rear seat. The takeoff was watched by the landowner who is an experienced private pilot. He said the aircraft left the ground about halfway along the strip and appeared to be climbing at a low speed with some lateral instability evidenced by minor wing rocking. Other witnesses described the aircraft as flying slower and lower than aircraft usually did when taking off from the strip. The aircraft crashed a few seconds later, just short of the M25 motorway that runs east-west beyond the northern end of the strip. The landowner had kept the aircraft in sight throughout its short flight. He described it having gained little height since leaving the ground, appearing to begin a turn to the right that was followed immediately by a sharp left wing drop with the aircraft descending rapidly to disappear from sight behind trees. There was an immediate explosion. The pilot and his young daughter died in the post-crash fire. The female passenger walked from the burning wreckage, calling for assistance to rescue those still in the wreckage. She was restrained by people who had arrived. This almost certainly saved her life because the fire rapidly spread out of control. The survivor provided valuable information about the short flight, although she did not recall the very last seconds. She was not a pilot or regular passenger and had not previously flown in the Bolkow or from this strip. She said that pre-flight activities appeared to her to be normal and the pilot did not seem to be concerned about the planned flight. He used a printed checklist and performed engine run-up checks before takeoff. She recalled being apprehensive about the take-off, being aware of the trees at the end of the strip, so was looking down during the actual take-off. Shortly after lift-off she sensed that the aircraft was no longer climbing and looked up to see the trees ahead. Her last memory was looking at the pilot and asking, “What’s wrong?” The pilot looked at her and was evidently concerned. He replied, “I don’t know.”
Flight Manual Recommendations The pilot had a total of 158 hours with 24 on type. He had flown about 11 hours in the past 90 days and 6 hours in the past 28 days. He had taken off from this strip on 11 flights prior to the accident. Only two of these had been towards the north, as was the accident flight. The weather was typical for late August, with fair weather cumulus clouds at 4,000 feet and excellent visibility. The surface wind was about 340/5-8kt, giving a headwind component for takeoff of about 5kt. The estimated takeoff mass of the Bolkow was 2,300 lbs, with the centre of gravity at the forward limit. The maximum takeoff mass was 2,640 lbs. A combined aircraft Operating Handbook and Flight Manual for this aircraft gave performance data at maximum mass and in still air conditions, giving a calculated distance of 493 metres required to clear 50 ft. This was from a hard, level runway and did not include any safety margin. Although not specifically stated in the Flight Manual the manufacturer’s performance figures are only valid if the recommended flying techniques are used. A ‘home made’ plasticized performance document found in the wreckage was damaged, but did include two performance figures, one believed to be a landing figure and the other believed to be takeoff distance to 50 ft, given as 480 metres. This equated to the Flight Manual figure for a temperature of +15 degrees C. This document did not appear to include any additional data, such as takeoff from grass. It is widely recommended that a factor of 20% be added to Flight Manual takeoff figures when operating from grass. This would increase the distance to 50 ft from 493 metres to 591 metres. Additionally, although private flights are not obliged to add further safety factors to performance figures, the advice from the CAA is to do so. A factor of 33% is recommended to allow for variations in ambient conditions and in pilot and aircraft performance. This would further increase the takeoff distance required for this aircraft at maximum mass to 786 metres – more than 100 metres greater than the actual length of this strip. The Flight Manual quoted a climb rate of 700ft/minute at the best climb speed of 70 kt with the flaps up. The advice was to retract takeoff flap only after clearing obstacles and at a safe altitude. The accident aircraft had completed an annual C of A inspection that included a flight test by a CAA approved flight test pilot conducted 18 days before the accident. The owner of the Bolkow had expressed a concern to the flight test pilot (who is also the light aircraft engineer who supervised the C of A inspection and an experienced Bolkow 207 owner) that the aircraft was not performing correctly, possibly because of lack of power. No such fault was found during the inspection or during the performance measurements made on the post-inspection flight test. The Bolkow 207 Operating Handbook describes the normal takeoff technique. This is to allow the tail to come to the horizontal position during the takeoff roll and then to lift off at about 55 kt. The aircraft is then to be levelled just above the ground until reaching the climb speed of 70 kt. This is the technique the pilot should have learnt during his tailwheel conversion course. The different ‘short field’ technique recommended in the Operating Handbook included the following: ‘Maintain a tail-low attitude (tail wheel on the ground) during the take-off roll and let the aeroplane fly itself off at a speed of approx. 43 to 49 KTS’ The Handbook then went on ‘Push control column and keep aeroplane just above the ground until reaching a flying speed of 70 KTS.’ For takeoff from a hard or soft surface or from a short strip the recommended climb speed was 70 kt. A friend of the Bolkow pilot who had flown with him in the Bolkow 207 described his impressions of the strip and the pilot’s techniques. He said the pilot was diligent and appeared to be comfortable operating the Bolkow from the strip. He said the Bolkow had a noticeably better takeoff and climb performance when operating from hard runways than it had when operating from the farm strip. He felt the farm strip was not long enough to allow the Bolkow to accelerate to climb speed, and would personally have preferred a longer strip. He thought the pilot would generally climb at a low airspeed before accelerating to climb speed after clearing the trees.
Recovered Data Data was downloaded from a GPS recovered from the wreckage. These data showed average groundspeed, lift-off point and climb profile against elapsed time for two takeoffs earlier in the month and for the accident flight. On 16 August the liftoff occurred at 44 kt groundspeed. This is assumed to be between 44 and 49 kt IAS allowing for a headwind of between zero and 5 kt. The groundspeed did not reach 65 kt until the aircraft had climbed above 300 feet agl. On 18 August the liftoff occurred at 37 kt groundspeed. It is probable that there was a 15 kt headwind component. The groundspeed reached a maximum of 58 kt about 20 ft agl and then decayed to 50 kt for the remainder of the climb to 300 feet agl. The accident flight profile was very similar, with liftoff at 44 kt groundspeed, reaching a maximum of 52 kt about 20 feet agl. The groundspeed then decreased as the aircraft climbed to a maximum of 95feet agl. The groundspeed continued to decay until the aircraft struck the ground at about 46 kt groundspeed. The above data seems to indicate that the pilot was following the Operating Handbook advice with regard to the actual takeoff until the aircraft left the ground. Thereafter he apparently disregarded the advice to remain just above the ground until the aircraft accelerated to the best climb speed of 70 KIAS. Instead he rotated the aircraft into a climb ATTITUDE and then attempted to climb out at low airspeed. Thus all his takeoffs from this 680 metre farm strip were marginal with the initial climbs performed close to the stall. Why the accident takeoff went fatally wrong we cannot know. Perhaps the aircraft was marginally heavier than previously, perhaps the temperature was a few degrees warmer, perhaps there was no headwind at all, perhaps the pilot rotated just a fraction earlier or more abruptly. The ultimate cause of this horrible accident is uncertain. What is more certain is that the pilot either did not understand the significance of the instruction in the Operating Handbook to hold the aircraft in ground effect while accelerating to a safe climbing speed or he decided to ignore this advice in order to operate from a strip of marginal length. The awful price paid by this family must surely encourage other pilots to study carefully the significance of lift induced drag and ground effect during takeoff (and landing). It is vital to make accurate safety allowances for each and every strip takeoff, no matter how often you have operated from the same strip. Pilots are invited to study our articles Accidents on Takeoff and Slow Flying, and take time to understand the message of these articles.
Ignorance will kill you.
Overconfidence Will Kill You — ARV Super 2 I had finished my RCAF ‘wings’ training on Harvards and returned to the UK to convert to Meteors. At the end of my Meteor F4 conversion I was 21 years old and had a total of just less than 300 hours in my logbook. The RAF recognised that pilots with 250-300 hours total experience were at a dangerous point in their careers, but this dictum escaped me. My end of course assessment contained the damning comment ‘Slight overconfidence’, signed by the Wing Commander of 215 Advanced Flying School at RAF Finningley. I had just enough sense to recognise that this was not a good assessment to carry to my first operational squadron so, despite dire warning from my fellows, I sought an interview with the Wing Commander to try to persuade him to amend the assessment. He glowered from behind his desk, opened my logbook and wrote something over the assessment therein. I saluted and left his office, feeling quite happy until I opened my log book and found that he had changed ‘Slight overconfidence’ by crossing that through and entering ‘Overconfident git’ in its place. I think I got the message!
Overconfidence can develop at any stage of a
pilot’s career and can be a killer. Those pilots who suffer from
overconfidence are unlikely to ever recognise that their ability is
considerably less than they think. The only way to overcome this personality
disorder is to recognise the fact when an instructor or a peer points it out.
‘Pull your neck in and develop some discipline and airmanship’
was the advice offered to me. A problem for recreational pilots is lack of
supervision of their flying once they have gained their PPL. (See our article
Supervision – the Missing Ingredient for a discussion of, and
suggestions on how to overcome, this problem.)
Sheep May Safely Graze?
Takeoff Factors
Fuel Factors
The Human Factor
Overconfidence will kill you.
Text and Photographs © 2008 Gremline & Hill House
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