"Conversion" of ILS approaches
 

I recently read an incident report in which a pilot describes how he had briefed for an ILS approach at a UK airport. At 12 miles, before he had captured the localiser, ATC informed him that the glideslope and NDB had both failed. He elected to "convert" the approach to localiser only.
At this particular airfield, the ILS and LLZ-only approaches are on seperate plates, and treated as seperate approaches. Is a change of approach legal at this late stage?

Depends
 

It depends on several things:

- Legal in whose eyes - Company, JAA?
- Had the possibility been briefed pre-APP?
- If not, was there time to brief the non GP APP and reset minimum etc. on long final?
- How was the weather? If it was VMC then it's less of a problem.

Generally - legal or not, a non GP APP takes some planning and a lot depends upon the crew's familiarity with the procedure and airfield. We are all human and a quick decision while under pressure to line up is not a good starter.

We teach:
1. Revise minima
2. Brief MAPt
3. Follow Advisory Heights

That is easy if the 2 approaches (ILS & LLZ) are on the same plate, takes a bit more time if on different plates. Therefore it's a command decision, based on time available, whether to convert. As far as legality is concerned, the only quibble is that you've been cleared for one approach and now wish to do another. Again depending on time available, a quick call to ATC should clear that up.

Legal, yes. There's no law that says a controller cannot do it. A controller faced with a situation like this where a navaid fails will offer whatever alternatives remain. Whether the pilot will accept the alternative is another matter. As Few Cloudy says, the weather will no doubt play an important factor in the Commander's decision but, ultimately, it's up to the crew on the aircraft and having dealt with a similar situation myself, it didn't surprise me that the aircraft that I had on frequncy wanted a bit of time to sort themselves out before making the approach.

What's interesting about Stifler's question is that both the GP and NDB failed. These are two completely different systems and it's hard to see how both could fail at the same time (without other significant failures). Nonethless, it could happen, but in this case it may take the only fix for the aerodrome out of play which might cause more problems for aircraft crews in terms of JAR-OPS requirements or whatever.