The detachment of the exhaust from its mounting would have been a startling event with plenty of noise and understandable uncertainty as to what was going on. Well done to the reporter for their quick decision to request a diversion due to obvious engine-related concerns, and all turned out well in the end. A couple of thoughts occurred to us as from the luxury of our post-event arm-chairs and so we offer them as food for thought.

First, we note the LARS Unit’s comment that the reporter couldn’t land at their location. Whilst we don’t have a detailed knowledge of the exact circumstances, and it may be that there were good reasons for them declining and suggesting an alternative airfield, in circumstances such as these where the engine condition is not known, pilots should think carefully about landing as expeditiously as possible rather than accept being told where to go by ATC. In this respect, it’s important to consider carefully whether a PAN or MAYDAY is the most appropriate call to make. A MAYDAY confers more urgency and an imperative to land at the nearest suitable airfield, which should not be refused. Subject to an airfield having a serviceable landing surface, better to land where you need to following an emergency and then argue the case afterwards than end up with an off-airfield forced landing. Don’t be afraid of using MAYDAY, you will not be admonished afterwards, but you may regret it if you opt just for PAN – a MAYDAY can be easily downgraded to a PAN if subsequent events indicate that urgency is not an issue.

Second, although all ended well at the subsequent diversion, don’t forget that the engine might fail at any point in such circumstances and so make sure you maintain sufficient height to perform a glide approach to the diversion airfield in case the worst happens.  The reporter themselves commented that they thought they had a cylinder failure (so a reason in itself for declaring a MAYDAY) which could have resulted in a seized engine at any point if that had been the case; fortunately it was not, but always consider the worst-case scenario.

Third, looking at the picture of the exhaust manifold, it looks as if there was some serious heat and potentially flame in the area of the dislodged clamp.  The reporter could not know that at the time but there are real dangers of fire in such circumstances and so that’s another reason for declaring a MAYDAY and getting on the ground as soon as possible with an engine or exhaust problem.

Finally, although the reporter didn’t know that the exhaust had separated at the time, loud noises like that with an otherwise functioning engine can be indicative of exhaust problems so do consider whether there may be a risk of CO poisoning as a result. CAA Safety Notice SN-2020/003, the associated Safety Animation, and the CAP2560 Leaflet about CO detectors highlight the importance of having one in the cockpit and, although passive ‘black-spot’ detectors are better than nothing, they do have an expiry date and there are better options available with active electronic versions that can be easily purchased online for relatively little money and have the additional benefit of an aural warning that will hopefully help in attracting attention to the presence of CO depending on cockpit noise levels and any headset active noise reduction if fitted and activated.

The reporter sent us a photograph of the offending manifold after the second separation incident and we passed it to our Engineering Programme Manager for his thoughts. He was cautious about making too many assumptions because he could not see the item in real life and so didn’t know what the pertinent factors were. However, he commented that the manifold connection stub looked quite short and so locating the exhaust properly and securely was vital because any slight movement or vibration would likely cause it to dislodge. In this respect, he wondered whether the clamp might have contaminates on its surfaces that were stopping it closing properly such that the 2 faces of the clamp were meeting before it was secure. He annotated the reporter’s photograph with some thoughts for others to consider during periodic checks of exhaust clamps such as this but we stress that these are generic thoughts rather than being specific comments on the actual installation which we have not seen.

In terms of the incident, as the reporter states themselves, there were a number of things that they could have done to be better prepared, not least in making sure that they had a Plan B for all the relevant options for departing their airfield (and who they might have to talk to), so that they would have an understanding of where ATC might route them if their primary plan was overtaken by events. The reporter had clearly been overcome by a series of relatively minor factors that, in isolation, are part of everyday aviation but had combined to distract them as they were ‘nibbled to death by ducks’ and got airborne in a rush.

In response to the infringement, the reporter received a ‘Just Culture’ letter from the CAA recommending some further training on TEM and associated issues. All airspace infringements must be taken seriously, but the CAA’s response was both proportionate and context aware, highlighting that things have come a long way in respect to how airspace infringements are now dealt with more pragmatically (in recognition that, although we must all endeavour to ensure we remain clear of airspace, mistakes do happen). Looking at the Airspace & Safety Initiative (ASI) website (as at June 2024), the statistics show that 76% of decisions so far in 2024 resulted in either no further action or an advisory letter as in this case. Of the remainder, 4% were required to do the online tutorial and test, and 15% were required to attend an Airspace Infringement Awareness Course (AIAC). The emphasis is on finding out what happened, learning lessons (both for the system and the pilot) and education rather than punishment – there’s a plethora of good material on the ASI website that’s well worth a visit to get some good tips on how to avoid infringing airspace.

This report raises some serious issues with how students are treated by controllers but, unfortunately, we’ve had no further response from the reporter to our requests for clarification. Because the reporter did not mention the airfield or the type of control being exercised at the time (ATCO, FISO, A/G?), not knowing the full circumstances qualifies any comments that we might make, and so all we can offer are some general thoughts below that may be worthy of note, especially with students in the circuit.

Notwithstanding the overriding premise that students shouldn’t really be asked to orbit in the circuit, if it was an ATCO doing so then they have a responsibility to ‘achieve the safe, orderly and expeditious flow of air traffic’ and they can issue information and instructions to achieve this. It is simply not possible for us to comment on whether a go-around or an orbit was the most appropriate option because we don’t know the circumstances. If it was a FISO or A/G airfield then that would be a different matter, and it would be up to the pilots to ensure safe integration, but the reporter says ‘the controller’ and so it should probably be assumed it was an ATCO.

CAP 493 Section 2: Ch 1 Para 19A says that ‘…instructions shall not be issued to aircraft in the final stages of approaching to land…’ but this is generally assumed to apply to aircraft on Final. In the situation described, the student was on base-leg and so there may have been few other options for the controller than to ask the student to orbit. We simply do not know the circumstances of the incident, what else was going on, and what the airspace construct was.

All that being said, and notwithstanding instructions from the controller, there was a certain responsibility on the joining twin’s pilot to satisfy SERA.3225(b) and ‘conform with or avoid the pattern of traffic formed by other aircraft in operation’ and so they ought to have given consideration to the student. If, for whatever reason, the controller had sequenced them, cleared them to join right-base, and they were below the student, then SERA.3210(c)(4)(i) says that ‘When two or more heavier-than-air aircraft are approaching an aerodrome or an operating site for the purpose of landing, aircraft at the higher level shall give way to aircraft at the lower level, but the latter shall not take advantage of this rule to cut in front of another which is in the final stages of an approach to land…’. So it’s not completely clear cut.

The reporter says that the student was ‘instructed’ to orbit. CAP413 Paras 2.34 and 11.5 refer to controllers having to make due allowance for the limited experience and ability of student pilots, and any pilot can refuse a request or instruction by saying ‘unable’ if they feel they cannot comply. Whether a student would feel confident enough to do so is a moot point though because they’re likely to interpret an ‘ask’ as an instruction anyway. But pilots should remember that they always have the option of telling ATC that they are ‘unable’ if they feel that they cannot comply with an instruction.

As the reporter comments, distraction by the oil issue during the walk-round was a key aspect but there are probably other things for us all to think about as well. Was the towbar painted a bright colour to attract attention? Do you conduct any ‘last chance’ checks before getting into the cockpit (such as chocks, towbar, tie-downs, earthing cables removed as appropriate)? Were there any other people who might have noticed the towbar as they taxied out? It’s easy to be clever in hindsight, but just a few seconds pause to stand back and think before getting in the cockpit can be worthwhile.

Accepting that aircraft might have tow-bars left on them if they are simply being manoeuvred out of the way and not intended to be flown, there is much to be said for the practice of ensuring that tow-bars should never be left connected to aircraft and unattended once the aircraft is out of the hangar and positioned in the desired place pre-flight. Good advice is that once your hand has touched a tow-bar that will be attached to an aircraft going to fly then your hand should not leave it until the tow-bar is replaced in its storage location (ideally a shadow board) after use. AAIB accident report G-SAJK/G-CDMH reflected similar circumstances and has useful associated lessons regarding improving the visibility of GA ground equipment that would be worth reviewing, and the associated Clued-Up article from the CAA about towbar colours is also an interesting read. Another AAIB report about towbars being left connected refers to one involving C172 G-BGIY and is also relevant. The QR codes give links to the associated articles.

Lastly, remember that incidents involving things falling off aircraft are subject to mandatory occurrence reporting (MOR) requirements as stated in IR 2015/1018 and accessed using the CAA Occurrence reporting portal via ECCAIRS2. If you’re involved in a similar incident then don’t forget to MOR it.

Ultimately, Class G airspace is a sharing environment in which neither military nor civil aviators have any priority over and above the Rules of the Air. We researched the NOTAMs mentioned and they were all ‘H’ series navigation warnings (which you just have to be aware of but don’t have to avoid) and not RA(T)s or TDAs (which you would have to avoid and would be ‘J’ series NOTAMs). Some useful links for understanding NOTAMs are the CAA Infringement Tutorial and UK AIP Gen 3.1 (Aeronautical Services) Table 3.6.3.4 which explains what each of the 18 NOTAM series types are (see below).

The specified locations of the 2 high-energy NOTAMs up to 20,000ft were applicable to operations at the reporter’s airfield, although [NOTAM 1] gave the blanket statement that associated military aircraft “…will avoid controlled airspace unless given permission to enter by appropriate ATSU” which implies that they would avoid the airfield ATZ. The reporter mentioned that their ATSU had tried to contact NATS to get further information but NATS would be unlikely to have any on a specific NOTAM and so that is probably why they received the response they did.  In fact, the 2 high-energy NOTAMs had the same contact number within their Section E details where more information should have been available to the ATSU (our assumption was that this number gave access to the exercise controllers who would have details of when aircraft might be using the areas and at what heights).

All that being said, one wonders how much research into airspace usage is conducted before the decision is made to plan military low-flying exercises. Why these specific locations were chosen we don’t know, but we’re all well aware that there could be high-energy fast-jets flying at low-level without NOTAMs at any time in most parts of the UK Class G airspace and so at least these NOTAMs were a step up from that in warning that there will be a higher concentrations in the specified areas over the associated periods. We doubt that the military will consult with [Airfield] before deciding on their exercise areas and issuing the associated warning NOTAMs, and military crews will be well-versed in understanding that [Airfield] is there and to be avoided. But there is a valid argument that local airfields and their training areas could be taken into account during military exercise planning such that likely conflicts due to concentrated military activity might be reduced. Perhaps there is also a case for GA training airfields to publish their own favoured training locations (if such exist) so that this information is available to all – military and other civil aviators alike?