Help on ILS systems please!!
 

Hi,

I am an aero engineering student, and have an assignment whereby i have to compile a report on the maintenance of ILS systems and present my findings.

This is for a reliability and maintenance course module, so the emphasis is on this side of things rather than how it works. i have to include:

1] a history of the developments made to the system to increase reliability

2] some details of maintenance schedules / MTBF / failure rates etc.

3] example of how incorrect maintenance of the system contributed to a near miss incident or aircraft crash.

I have searched to web and so far havent found any relevant info. I would appreciate it if any of you guys could point me in the right direction.

Cheers,
Phil :)

Have a look at some of OzExpat's recent posts. He has been doing a review of ILS problems following on from the ANZ review done after the Apia 767 incident a couple of years ago.

Regards,

JT

Thanks for the plug John. There certainly IS a fair amount of info on the net about LLZ and/or GP faults.

empty pockets... for all the other info you need, you might be better off going to the websites for the various equipment manufacturers.

cheers guys. followed the links on Ozexpats messages and found pretty much all I needed from flightsafety.org. v. useful, if a little unnerving!

It is not unheard of for technicians to disable the monitors and alarms in order to stop those pesky trip outs.

Years ago, I was aware of a Cat 2 ILS which didnt conform to Cat 1 standards whose monitors were disabled.

I also know of LLZ beams drifting by as much as 45 degrees in heavy rain. It was uncertain whether it was beam width or direction which was out of tolerance. Luckily the aircraft became visual at approx. 1000' agl.
The only way this can happen is if the monitors and alarms are disabled - otherwise there would have been a transmitter change and if this second transmitter was also out of tolerance, the LLZ and G/S would have shut down.

Likewise with G/S signals which have a tendency to drift with water table height. The temptation to disable the monitors and alarms in order to have a good nights sleep must be overwhelming.

From memory, it is an ICAO recomendation that ILS's are flight checked every 120 days. Of course with modern electronics this ferquency is ludicrous. Nevertheless, there are still ILS sites with 1970's vintage equipment who hardly ever do flight checks because of financial constraints.

It is at these locations where there is a liklihood of technical hanky panky. We are also fortunate that the weather is for the most part nearly always benign in these places.

I also wonder whether the present trend for flight checking on a commercial basis can lead to a compromise in standards.

Its been more than 12 years since I had first hand information - however, the sceptic in me has difficulty in accepting that things have got any better.