Confidential Human Factors
Incident Reporting Programme
The Charity
Aviation
Maritime
ATC847
Initial Report
As an ATCO operating at a busy Radar equipped Civil Aerodrome in Class G Airspace, I am well versed with the idiosyncrasies of Class G operations and the plethora of different flying machines that operate within it. Having spent time attempting to ascertain the relevant desk officer in DAP and their contact details, my apologies for choosing this route as a 100% reliable back-up.
It is pleasing to see the increased use of Transponders within the glider community, and for that they should be thanked. However, with the 7000 Conspicuity squawk the one most often selected, and the Mode S (if fitted) not really indicating the difference between a GA aircraft and a Glider, I would opine that now is the time to allocate a discrete unverified code for Gliders to select.
It is incredibly difficult to ascertain the difference between a GA powered aircraft on a 7000 code, likely to remain straight and level in flight point to point routing, and a Glider, likely to reverse course and thermal at any time. This makes managing conflicts, especially on final approach or within instrument procedures, incredibly difficult.
At our unit, the introduction of the FMC had a massive impact on conflict resolution and was the single biggest safety enhancement of the last decade. I would opine, the ability to differentiate between powered and un-powered flying machines, from an unverified squawk, would be incredibly useful to aid in managing airborne conflicts for ALL Class G Air Navigation Service Providers.
Supplementary; we know aircraft that have Mode S transponders as they are displayed on our screens with an Orange Dash next to them. I’m still surprised with the sheer volume of aircraft we see transponding 7000 but without Mode C data transmitted, when we know the aircraft is so equipped. CAA Safety Department could really help the situation by focusing education on this matter; to ensure owners and aircraft hires are fully aware of the aircraft’s systems and how to operate them. When in communication with such aircraft, when challenged, 90% of the time Altitude is fitted and just not selected. I routinely see several Mode S equipped aircraft operating within the vicinity of the [Location], squawking aerobatics but with the Altitude not selected. Electronic Conspicuity is one of the many mitigations for the airborne collision risk in Class G airspace. I’d like to see the CAA take a more aggressive stance on those that actively choose not to participate; either deliberately or through lack of knowledge.
BGA Comment
Transponder devices, whether Mode S, ADS-B or other are of course an element of a future where there needs to be greater integration. Where the sky is busy with traffic that needs protection, transponders can of course be a requirement and we agree that it could be useful for a controller to understand which is a glider. We also wonder if some devices might already be linked to an aircraft type and push out data such as ‘glider’ that could be interpreted from the incoming transponder data into information on the controller’s screen.
CHIRP Comment
The idea of a glider conspicuity code seems a reasonable one, accepting that there might be limitations in its utility at present due to the numerous gliders that do not have transponders. In the past, battery technology was such that not many gliders had transponders and, if they did, they were only selectively used in order to save power for other equipment. These days though, battery technology has greatly improved and so more glider owners are probably able to instal and use transponders if they wished to do so. We don’t know what the take-up is for transponders in gliders but, as battery/power sources become more efficient and more gliders might in future have transponders fitted as a result, a discrete glider transponder code could be a useful adjunct to managing airspace if we can get over the power limitations and cost of installation on more than a few high-end gliders. Noting that the BGA are overall supportive of the idea, we have approached the CAA for their view but still await a response at the time of writing.
Regarding aircraft not using Mode C, SERA.13010 ‘Pressure-altitude-derived information’ is clear within its Para (a) in stating: “When the aircraft carries serviceable Mode C equipment, the pilot shall continuously operate this mode unless otherwise dictated by ATC”. If an ATCO observes an aircraft operating without Mode C when they could reasonably expect it to be so equipped (i.e. when displaying Mode S for example), then this is potentially in contravention of SERA.13010 and could be reported using the Alleged Breach of Air Navigation Law (ABANL) process already available to controllers and the public.
There is a belief by some aerobatic pilots that it is better to turn off Mode C if conducting aerobatics near airport approach paths in order to reduce TCAS interactions; however, there is little evidence as to this being a real rather than perceived concern. Aside from anecdotal comments regarding Mode C being turned off, we have asked the CAA if they have any statistics or evidence that point to interactions between aerobatic aircraft squawking Mode C and TCAS-equipped commercial aircraft on approach to airports. If there are examples of such interactions then evidence needs to be generated before any rule change can be made that might perhaps permit a dispensation for aerobatic aircraft to not squawk Mode C in some locations.
Key Issues relating to this report
Dirty Dozen Human Factors
The following ‘Dirty Dozen’ Human Factors elements were a key part of the CHIRP discussions about this report and are intended to provide food for thought when considering aspects that might be pertinent in similar circumstances.
- Awareness – Improvement of controller SA by introduction of a glider conspicuity code.
- Complacency – Increased risk through operating with Mode C selected off.
- Deviation – Aircraft operating without Mode C selected, and controllers not reporting such instances.