Gremline Flight Safety Report: CFIT - Fatal Mountain Flying Accident

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the gremline digest —  controlled flight into terrain #3

Controlled Flight Into Terrain (CFIT) - A Fatal Mountain Flying Accident
For an Introduction to CFIT and examples involving a Jodel DR1050 and a Robinson R44, Click Here. For a further example involving low flying in a Jet Provost Click Here.


 A classic example of a CFIT accident occurred late on a Friday afternoon in February when a Cessna 172M with three people on board struck the vertical rock face of a mountain in Wales. The aircraft hit just 155 feet below the cloud-covered 2,713 ft summit and 67 feet below the top of the rock face. The wreckage fell 200 feet before coming to rest on a steep heather-covered slope at the base of the rock face. All three occupants died in the impact.


The commander of the aircraft held a CPL with Assistant Flying Instructor’s Rating and had 1002 hours as pilot. He had flown 180 hours in the last 90 days and 62 hours in the last 28 days. He had also accumulated 3,645 hours as a navigator in the Royal Air Force, which he left four years before the accident. The pilot who hired the aircraft, and is likely to have been handling the aircraft during the accident flight, had a PPL issued four years before the accident. He held a current IMC rating and had a total of 176 flying hour with 6 hours on type. The third occupant was a student pilot who sat in a rear seat and probably took no active part in the flight. The hirer had not flown for two and a half months so had arranged for the AFI to fly with him to satisfy the operator’s 4 weeks currency requirement.
      The three pilots boarded the aircraft at about 15.10 hrs on 12 February and took off shortly after 15.15 hrs. The airfield is at 233 ft above mean sea level in a river valley with high ground on either side of the valley. There was a frontal zone to the north of the airfield moving very slowly southeast. A cloudy southerly airsteam covered Wales with a broken cloudbase at 1500 feet and overcast between 2,000 and 2,500 feet amsl. The visibility was between 2,000 and 5,000 metres with a light southerly wind at 2,000 feet. The nearest observation to the accident site was at Lake Vyrnwy 1,180 ft amsl about 7 nm south-west. They recorded an overcast at 500 ft agl, lowering to 400 ft agl (about 1,600 ft amsl). The low level wind flow over the mountains is complex but it is likely that the cloud base at the accident site was about 2,100 ft amsl, with the surrounding higher ground in cloud.


Clee Hill Radar recorded secondary returns from the Cessna beginning at 15.25 hrs as the aircraft was at 1,558 feet 3 nm west of the airfield tracking about 343° (M) with a groundspeed of 90 kt as it climbed to about 2,000 ft amsl. It continued to track north-west until it descended into a valley at 15.34 hrs and contact was lost as the aircraft descended below 1,558 ft amsl. This valley is orientated north-west with ground on either side rising to about 1,970 ft amsl. Eyewitnesses saw the aircraft flying up the valley paralleling a road and below the level of the valley side. The tops of the adjacent hills were was not in cloud at this time.
      Radar contact was regained at 15.36 hrs as the aircraft reached 2,158 ft about 1 nm north of the valley end. The aircraft tracked north and climbed. It was at 2,358 ft amsl when the rate of climb increased to 725 feet per minute and the groundspeed dropped from 85 kt to about 45 kt. The last radar contact was at 15.36.58 hrs at 2,558 ft amsl about 600 metres north of the place where the wreckage was found. The ground in the immediate vicinity rose to 2,625 ft amsl.
      The airfield staff became concerned when the aircraft had not returned by 16.30 hrs and alerted the Distress and Diversion (D&D) cell at the London Area and Terminal Control Centre. The D&D controller began overdue action and alerted the Rescue Co-ordination Centre (RCC). The last position from the recorded radar tack was passed to the RCC who alerted the rescue helicopter and the Mountain Rescue Team (MRT) at RAF Valley on Anglesey. The weather in the crash area precluded a helicopter search but the MRT met local police and began the search. The visibility in the search area was 200 metres in fog. The wreckage was located at 01.26 hrs within half a mile of the last radar contact. The MRT reported that the aircraft had apparently flown into steeply rising ground and then tumbled back down the slope.
      The wreckage was recovered to AAIB Farnborough with the assistance of RAF St Athan Aircraft Recovery and Transportation Flight and the RAF Stafford Mountain Rescue Team. Detailed analysis of the wreckage and evidence from the point of impact led to the conclusion that the aircraft struck the rock face in a nose-up attitude while steeply banked to the right. The meteorological data recorded at the time of impact makes it likely that the aircraft was in cloud when it hit the rock face. There was no evidence of any pre-impact malfunction of the aircraft or its systems.



Editor’s Comments
The facts in this article are based on UK Air Accidents Investigation Branch Field Investigation Reference EW/C99/2/3 which source is gratefully acknowledged. The following comments are those of the editor and do not necessarily reflect the views of either the AAIB or the UK Civil Aviation Authority (CAA).
      CFIT accidents in mountains are the easiest of all general aviation accidents to experience at first hand! Most general aviation aircraft have limited performance capabilities with little excess power available, poor rates of climb, feeble power/weight ratios and are flown by pilots who are neither trained nor experienced in mountain flying. This makes it all too easy to wander into a cul de sac and become fatally trapped there. Mountain flying is not a skill you are born with and cannot be developed by trial and error. Your first error is likely to be fatal. If you are going to fly among mountains then you need to know something about MOUNTAIN FLYING. This requires specific knowledge and skills you have not acquired in your previous flying. I recommend reading up on the subject in Chapter 7 of “Flying the Edge” by the late Captain Brian McAllister (Available from our
Bookshop). Reading and understanding this chapter will not qualify you to set off into the mountains but it may make you realise that you need some specialist training before doing so. The rest of the book is also well worth reading.
      Mountains make their own weather! The weather can change very, very quickly in the mountains and you must always leave yourself a planned escape route. Climbing a sailplane in excess of 1,500 feet per minute in the standing waves over mountains and going up to over 25,000 feet is great fun. Getting rattled around in the rotor off a mountain ridge or blundering into the down side of a standing wave with the VSI off the bottom of the scale is not quite so enjoyable.
      Flying a GA aircraft towards a mountain ridge only to find that the ground is climbing faster than your aircraft can achieve is a lesson not to be forgotten. Do you KNOW what the maximum rate of climb is for your aircraft flying at Vy? How about at Vx? What’s the difference? You don’t need the figures in the Manual that were recorded when the aircraft, engine and propeller were all brand new and being flown by the company test pilot, and then possibly ‘rounded up’ by the marketing department. You need the figures that your aircraft can achieve now with a slightly tired engine, just a few nicks in the prop and probably a few layers of paint acquired in the past twenty years. At sea level with three people aboard? How about at 2,500 feet amsl on a hot summer day in a downdraft off an adjacent mountain? Do you know how your Vx changes with an increase in altitude?


It can be very tempting to bumble up a valley without a care in the world, enjoying the scenery with your friends. Everything can go pear-shaped very quickly when you are near high ground. The majority of GA aircraft have narrow performance margins. Mountain flying always demands special skills. Keep out of the mountains until you have been taught those skills.



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