Nick Heard

Accident Analysis

With Nick Heard

Accident Analysis

Tragic consequences of being ‘stuck on top of cloud’

Safety Editor Nick Heard analyses a crash involving a Mudry CAP 10 aircraft that killed pilot and passenger, and looks at the chain of events that led to the accident. Plus, how GA pilots caught in a similar situation could respond

Aircraft Type and Registration: Mudry Cap 10B, G-BXBU
Date & Time (UTC): 12 August 2021 at 0920 hr
Location: Lower Colley Farm, Buckland St Mary, Somerset

Persons on Board: Crew: one Passengers: one
Commander’s Licence: Private Pilots Licence

Commander’s Age: 69
Commander’s Flying Experience: 1,411 hours (of which 648 were on type)

The pilot found himself stuck above cloud during a cross-country flight under Visual Flight Rules (VFR). After contacting the Distress & Diversion Cell for assistance he was transferred to the radar frequency of a nearby airport, at which the cloud base was below the minimum required for the approach offered. 

The pilot, who was not qualified to fly in cloud, lost control of the aircraft during the subsequent descent, and it was destroyed when it hit a tree. Both occupants were fatally injured. 

The investigation found that air traffic service providers did not obtain or exchange sufficient information about the aircraft and its pilot to enable adequate assistance to be provided. There was an absence of active decision making by those providers, and uncertainty between units about their respective roles and responsibilities. 

Seven Safety Recommendations are made to address shortcomings identified in the provision of air traffic services in an emergency. 

Mudry CAP aciident
Image: AAIB

History of the flight

G-BXBU departed Watchford Farm in Somerset, which was the aircraft’s home base, at 0704 on 12 August 2021, with the pilot and one passenger on board. Their intention was to fly to St Mary’s on the Isles of Scilly for a day trip before returning to Watchford Farm later that afternoon. At the time of departure, the local weather was described by witnesses as clear skies with good visibility. 

After departure, the aircraft flew south-westerly as planned, towards Cornwall. As the aircraft passed north of Culdrose, it began a descent to 1,000ft over the sea, before turning right to head east away from the planned destination. 

It continued in a north-easterly direction, passing to the north of Torquay then out over Lyme Bay. While over the sea, the aircraft reached a minimum of 320ft momentarily before completing three 180° turns and two 360° orbits. It then began to fly north from Lyme Regis toward Watchford Farm climbing to a peak altitude of 8,200ft amsl. 

At approximately 0905 the pilot called Dunkeswell Radio, using the words ‘PAN, PAN, PAN’ (indicating urgency), asking about the weather conditions at the airfield and stating that he was unable to land at Watchford Farm because he was stuck above cloud. The A/G operator at Dunkeswell replied that the weather at the airfield was poor – the cloud base was ‘on the deck’ and the visibility was 400 m. 

He suggested the pilot contact Exeter Radar or the Distress and Diversion (D&D) Cell on the emergency frequency 121.5 MHz. 

The pilot made another PAN call on 121.5 MHz at 0911, stating he was in ‘real trouble’ as he was stuck above thick cloud and he didn’t know what to do. He finished his radio transmission by stating, “I need to divert to somewhere close to me where I can land.” Several witnesses in other aircraft who heard the call described the pilot sounding anxious and stressed. 

The PAN call was initially acknowledged by two commercial aircraft in the vicinity prior to a response from the D&D controller who stated, “… your PAN is acknowledged”. In response, the pilot stated his altitude was 7,500ft and that he had a fuel endurance of 1.5 hrs. 

The transponder on G-BXBU had not been used throughout the flight, but at the request of the D&D controller the pilot switched it on and set the emergency squawk of 7700. 

At the time G-BXBU declared an emergency, there was a military jet holding in the vicinity of Exeter Airport – where it had departed 28 minutes earlier. The aircraft had experienced a technical fault after take-off which was subsequently resolved. The aircraft was holding to burn fuel and reduce its landing weight, prior to returning to land at Exeter. 

G-BXBU had been seen by controllers on Exeter’s primary radar but there was no altitude information displayed as the transponder was not switched on. Exeter ATC was concerned about a potential conflict with the military jet, which was holding between 3,000 and 4,000ft. 

While G-BXBU’s initial contact with the D&D controller was ongoing, a phone call between the Exeter Radar assistant and the D&D support controller took place between 0912 and 0914.

The D&D controller understood the D&D support controller to mean that the Exeter Air Traffic Service Unit (ATSU) had assessed that aerodrome as suitable for a diversion by the pilot of G-BXBU.

He believed Exeter heard the ‘PAN’ call on 121.5 MHz and that the reason for Exeter’s phone call was solely to offer help to G-BXBU. He was not aware of their concern of a potential conflict with the military jet, nor that the D&D support controller was speaking to an assistant. 

When the D&D support controller told the D&D controller that Exeter was willing to take G-BXBU, the D&D controller advised the pilot of this one second later. The location of the D&D controller and the D&D support controller was such that the controller could not overhear the conversation with the Exeter assistant directly. The Exeter assistant did not identify herself as such during the phone call, contrary to operating procedures. 

Although the emergency squawk of 7700 was visible on the radar controller’s screen, G-BXBU was transferred to Exeter before anyone with controlling authority at that aerodrome had been made aware the aircraft was diverting in an emergency. 

There was no formal radar handover from the D&D controller and the suitability of Exeter, in particular the weather conditions at the airfield, were not discussed at any point by either the Exeter assistant, D&D support controller or the D&D controller. 

When the pilot of G-BXBU made initial contact with the Exeter controller he confirmed his emergency ‘PAN’ status and stated, “have been diverted”. 

The controller initially advised she would give him vectors for an ILS approach for Runway 26 at Exeter. The pilot asked her to repeat her transmission and in her response the controller advised she would give vectors for a Surveillance Radar Approach (SRA), instructing him to fly a radar heading of 220°.

The controller recalled that this change in clearance was prompted by input from a colleague who was in the room and witnessed her communications with G-BXBU. The pilot asked her to confirm the cloud base at Exeter, to which she replied the visibility was six km and the cloud was broken at 500ft. The controller commented that she was surprised to be asked about the weather conditions at this point, as she would have expected the pilot to have this information before diverting. 

At 0914 the controller observed the aircraft descending and not maintaining the assigned heading. 

At 0916 the radar track showed the aircraft levelling briefly around 4,000ft. Without having noticed this, the controller instructed G-BXBU to descend to 2,600ft, which was the minimum safe altitude, aiming to prevent the aircraft descending below that. 

The last radio transmission from the pilot was ‘descending two thousand six hundred, you want me on two three zero?’. The last radar return was at 0917, and showed the aircraft at 2,700 ft. 

Several ear witnesses nearby described a loud engine noise prior to an impact. 

At 0920, Devon and Cornwall police received a report of an aircraft accident. Emergency services found that both occupants had been fatally injured. 

Pilot’s background

The pilot had a total flight time of just over 1,400 hr. He held a valid PPL(A) with a valid Single Engine Piston (SEP) rating issued by the CAA, and his medical was in date. He had completed a total of 1.5 hr of instrument flying during his initial PPL training 21 years earlier. 
The pilot had owned G-BXBU since 2014 and it had been hangared at Watchford Farm since 2015. He was described by flying acquaintances as a ‘fair weather’ flyer. It was reported that he did not routinely request an ATC service, nor did he operate the aircraft’s transponder. 

Decision to fly

When the pilot checked the weather information online at 0519, it indicated that at Exeter there would be light south-westerly winds throughout the morning, with less than 20% chance of rain. Weather forecasts for aerodromes along the planned route deteriorated throughout the morning and the extent of the poor weather was not reflected in the weather information available at 0600. 

It was not possible to establish the extent of any additional weather planning the pilot carried out before departure. The forecasts available when he left home differed significantly from those that became available before G-BXBU took off. 

There were clear skies when the flight departed, which may have reinforced the pilot’s belief the conditions were suitable for the intended flight. Nevertheless, there was sufficient ambiguity or indication of poor weather to suggest conditions might not be suitable for VFR flying.

Nick’s Analysis

This terrible accident has been the subject of some heated debate on the FLYER Forum. The AAIB report itself is more than 40 pages long and includes a great deal of analysis about the factors that led to the crash, together with several recommendations to the CAA.

The AAIB report also includes the full transcripts of radio and telephone conversations during the critical period, which are too long for this article. I recommend that you read the full report to see how – as in all accidents – a chain of events comes together to create the conditions for this awful crash which killed two people.

My analysis will concentrate on what we, as GA pilots, might do to avoid getting ourselves into such a position as the pilot of this CAP 10, and how we might extricate ourselves from this predicament safely.

The pilot was relatively experienced and had owned and flown his CAP 10 for several years. However, he was a VFR pilot only, with his only recorded instrument flying training completed during his PPL course years ago.

The CAP 10 that he owned was really not fitted out for flying in IMC, with a very basic artificial horizon that probably worked fine, but which required a lot of practice to use and interpret competently. He also appeared to not be in the habit of using his transponder. 

The pilot checked the weather forecast early in the morning but before the first 0600 TAFs had been disseminated. Checking so early probably meant that there were no TAFs available for the coming day for airports that may not have been open overnight. There is nothing wrong with that, but it just makes making a proper weather assessment a bit harder.

However, a bit more research might have revealed the presence of the moist south-westerly airflow that will often leave the West Country under mist, fog, and low cloud. 

However, the weather was good when he took off and proceeded towards St Mary’s. Unfortunately that situation changed fairly early into the flight. The pilot apparently flew at around 300ft over the sea before climbing – presumably still VMC – to end up at around 8,000ft and on top of cloud.

The pilot made a PAN call to Dunkeswell, explaining his predicament. The Dunkeswell radio operator made a good call to advise that the weather there was clearly unsuitable and gave him the excellent advice to contact D&D on 121.5. 

The pilot duly did so and the situation might well have been resolved from that point. Unfortunately, following a sequence of miscommunication and misunderstanding between D&D and ATC at Exeter, the pilot was directed to descend into cloud to fly an instrument approach at Exeter, a manoeuvre that he was not qualified to fly in weather conditions that were far beyond his training and experience, in an aircraft barely fitted out with the necessary equipment for such an approach. 

Not unexpectedly he became disorientated in cloud and lost control of the aircraft, leading to the crash a few minutes later.

Stay calm and use the time available

Let’s go back to the position where the pilot found himself stuck on top of cloud. At that moment there was clearly a problem in landing at an airfield in the vicinity, but with 90 minutes of fuel available there was time for thinking. 

So here is my first advice when caught out in a tricky situation while airborne such as this one:

Time available is usually dictated by fuel, but possibly by weather or approaching darkness, or the loss of the engine. But in this case, there was time to think and assess. Many accidents are caused by pilots acting too quickly – take your time if you can.

Do not let the situation get worse

The pilot was in no immediate danger while VMC on top of cloud. The danger only occurred when he entered cloud. So, as a VFR pilot, do not enter cloud. If necessary fly in circles to stay VMC. 

Never accept instructions from ATC that will put you beyond your capabilities, such as into cloud. Advise ATC that you are unable to comply due to weather.

Get some help

The call to D&D was the best course of action – even if D&D don’t get you immediately, passing airliners may well intervene to help, as in this case. Now in this accident, things went wrong between D&D and ATC, and I am sure that those events will not happen again in the future.

D&D will generally offer the best assistance. It has information of airfields across the country, including weather and frequencies. In normal circumstances, I believe it would have given the CAP 10 pilot all the information that he needed to divert, probably some distance to the north-east where the weather was clearly much better, and we would not be reading this accident report.

Use D&D to help you out. And you should be using a transponder!

Make a decision and act

Decide the best course of action and make a plan. Keep options open for amending the plan as you execute it, obeying all the rules above. Keep using the help available to make things as easy as possible for yourself.

This advice is aimed primarily at the VFR pilot with little instrument training. It is always worth getting some instrument training in the UK, if only to learn or remind yourself as to how to at least maintain a constant attitude on instruments and complete a 180° turn (as you flew on your PPL Skill Test). You don’t need to do a complete course of training, though it’s a good idea.

In summary:

  • Check weather carefully, especially for early flying.
  • If you get into some sort of tricky situation while airborne:
    • Stay calm and use the time available
    • Don’t make things worse – stay VMC at all costs 
    • Get help – use D&D
    • Decide and act
  • Get some instrument flying training, just in case.

See also: Nick’s comments on various accident reports. Click here


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