Jim,
I believe that by law one is only allowed to fly a 'published' instrument approach
I assume you mean that if, for example, you have a 15DME arc as part of some procedure, you must fly that using your DME? If that's what you mean, it's not quite correct. Essentially, you have to fly the track and profile which says on the plate, but how you do it is entirely up to you. You will notice for instance that airliners fly with reference to their nav solution, which is determined from a number of inputs duly weighted and filtered.
Another example closer to the GA world: flying a procedure once where the MAP was overhead an NDB which was inop. By your reasoning, that procedure could not be flown--in actual fact, you work out the MAP from whichever other information you have--it could be a DME reading or a GPS fix or an INS solution or your mom on the phone[*], it doesn't matter.
[*] as long as she is certified nav equipment.
I was responding to the suggestion in a previous post that ADF and VOR are not the instruments to be used for navigation in this situation. I don't agree with the earlier post
The above notwithstanding, which hopefully explains the difference between what you have to carry and what you can use, a typical example is you're cleared on a SID and as soon as you're airborne and switch over to radar, they give you a direct to some reporting point 80nm away. You could of course work out the offset angle from some VOR and fly a series of VORDME cross-cuts or whatever, but the controller is not going to be impressed one bit. In practise and in order of preference you either hit D-> on your GPS, request a vector, or decline the clearance. The last two are likely to annoy the controller, especially the latter since it now means he cannot get you out of the way as he was hoping to make space for someone else.
Bottom line, you use whatever works best to get you there safely and efficiently.
If you have done your IR in the UK, you will have noticed that the vast majority of IR instructors (+ examiners) there do not have any actual IFR experience outside their training environment so sometimes you have to take their words with a pinch of salt or two.
Dave,
Well I'm doing my PPL at the moment, 7 hours solo, first solo nav after 15, in fact, I did it today
Ah, Ok. Well, thanks for sharing your knowledge with us.
This is about someone who's just passed their PPL, and obviously hasn't been taught properly and wants advice
So that's where you come in with less than half his meagre experience and put him right. Isn't that quaint!
