I've found that the supposedly "tried and tested" VOR/DME and ADF sometimes fail on me (I fly a SPIFR aircraft). Sometimes they are under known maintenance or for unknown reasons fail to ident. Some parts of the UK are very poorly served with appropriate beacons. The CAA have announced that their support for NDBs will soon cease. In some cases, if one beacon fails, that's it, no "conventional" cover and (in the absence of GPS) a DR fallback is the only option.
On the other hand, I've flown aircraft equipped with GPS in one form or another since 1991. I think I've only ever had a complete GPS failure once, probably caused by NOTAM'd jamming trials that were taking place in Wales at that time.
My concern is that the "multifunctional" radio/nav equipment switchery in some modern aircraft is so complicated that it can be counterintuitive; to the extent that a self induced failure is by no means out of the question. However, when I changed aircraft types with unfamiliar nav. kit, in the absence of someone to teach me first hand, I downloaded the manuals and read them, then sat in the aircraft with an external power supply plugged in. I didn't give up until I was happy with the equipment. Surely this is what we should all be prepared to do, or stay on the ground until competent?
Having said all this, obviously a sound knowledge of basic nav techniques is essential or there could be no DR fallback plan.
Last edited by ShyTorque; 28th December 2008 at 22:29.
Reason: Bad spelling.