RNP approaches / no more than 90 degree turn to IAF

I should add some examiners, even wanted the ADF audio on

The only proper way of flying NDB approach

@arj1 I do think we are overthinking this! Am not aware of any examiner who demands you dead reckon and self position from CIT to ADSON. It is good practice to explain this 110o degree fly by limitation in the context of jet traffic, but for the purposes of a piston IR (whether the RNAV is well or badly designed am not in a position to judge) where the examiner wants you to demonstrate an NDB hold followed by a procedural RNP LNAV she/he expects you, when cleared to route ADSON, to activate the approach and as a good child of the magenta, follow the magenta.

Cranfield EGTC was the examiner base for the CAA and I would guess around a third of UK IRs conducted their initial IR there. We should be grateful that we no longer have to fly an asymmetric NDB/DME (beacon being off field adds to the excitement), and if we failed to identify the DME, it then turned into a timed raw no DME NDB followed by a circle to land. Obviously if you forgot to start the timer either outbound or at the FAF, it was a failed test component. Those were the days when around half IR attempts were partials, pour l’encouragement des autres :)

I should add some examiners, even wanted the ADF audio on, as before glass there wasn’t a NO DATA failure indication mode.

arj1 wrote:

so all I want to understand is what the regulation is and where in the UK/EU regs it is specified, so I could relay that to a potential examiner…

I understand that. But unfortunately the regs only say “fly the procedure”. You’ll find no regulation about the maximum turn angle just as you will find no regulation about racetrack or hold entries. If the procedure is poorly documented and/or designed, then you may have a problem.

The 110o fly by turn limitation on the IAF is designed to ensure the airplane is not messaged by the GPS too early and then misses the intermediate fix, and is not able to have a stable run in to the FAF. In practice puddle-jumpers operating at 110-120KIAS setting course for ADSON from CIT will not experience this problem of geometry, although under strong north westerly winds (40 knots?) it might occur. EGTC and EGBJ probably have a high proportion of IR practical/revalidation tests in the UK, and practically the expectation is to navigate to ADSON on leaving CIT. Similarly, GST to LAPKU.

Additionally, you are in receipt of that glorious british chocolate tea pot service, the non radar procedural service.(Although EGBJ is offering radar some times). Launching off on some home made self positioning to ensure you do not exceed 110o turn at ADSON, while perhaps with honorable intentions, is not that practical under a procedural service.

All IREs expect you route CIT ADSON unless you turn up in a Lear Jet.

That is probably correct as the turn between the route to ADSON from the outbound of the hold and the 141° course from ADSON to the IF looks to be around 110°.

Looking again, the depicted cake slice centre is not ADSON as expected, but TC211.
So in compliance you can route directly to ADSON for the IAF and make the turn.
No fuss req

arj1 wrote:

the moment you exit the hold (and start flying west of the FAT), you are in the correct sector for ADSON. Please note that this pie diagram has got TC21I in the top right corner, so technically it is in the right sector (unlike Jepp where there is no reference to the IF in the pie diagram) and could fly directly to ADSON (especially if APP tells you "cleared for the procedure via ADSON, report ADSON).

Ah, ok. I still would not do it as I know that the procedure is designed under the assumption that you do not turn more than 110° at ADSON.

I may be wrong but just because there is a segment around ADSON doesn’t mean you must use ADSON as your IAF. The piece of the pie only represents the minimum safe altitude in that section in the same way as the MSA circle based on the ARP may be split into several minimum sector altitudes.
IMO there is no reason, in class G with no ATS that you shouldn’t use one of the other IAFs.

If this were a US approach, my understanding of the purpose of a TAA is that in the TAA segment, one may use RNAV to navigate to the IAF involved and not need radar vectors. Anywhere inside the TAA 25 NM segment should be allowed for navigation to the IAF. I would self navigate to ADSON and choose to approach ADSON on a course that would need approximately a 90 degree turn to the leg to TC21I. Any RNAV system with a moving map would make this easy.

Of course, this procedure would not show up in the US and a conventional navigation aid would not be used in the MAP procedure (CIT and the DTY 115R) . There would also most likely be a hold at TC21I that would be used for the MAP and as an HILPT. Also the TAA segment for right base entry would never be lower than the intermediate segment altitude.