A 'routine' flight check of ILS (and PAR for that matter) should be carried out every 180 days. Limited extensions to this may be granted if the weather is unsuitable for the flight check. If there is an incident where the performance of the ILS might be taken into account, a special flight check may be called for.
. . . . such as post-accident. Have known four occasions when that has been necessary.
Also if you do some significant maintenance to the antenna arrays or such then it will need calibrating, and in the case of a Cat II/III system, run for so many hours at Cat I before it can be used for Cat II/III.
Is that because the calibrater flies the reciprocal? I remember watching at LHR on easterlies, oh so many years ago, and a lot if sniffy Umerikans (queueing up in their 707s, DC7Cs, DC8s and Convair Coronardos ) wouldn't accept a take-off clearance (with an early turn out) into the face of the calibrating Dove.
Last edited by Cumulo-nimbus on Fri Jan 04, 2013 7:53 am, edited 2 times in total.
Banking: a licence to create money. Let's be out of the bureaucratic monstrosity; and EASA too!
Pugh Pugh wrote:Please do tell, Vintage, of the Near and Far.
For the terminally bored . . . . . Near Field Monitor - antenna on a small pole in front of the localiser. It is that which detects an infringement of the Critical Area around the loc (or more correctly, it detects a disruption to the loc signal). The loc then drops to standby and then off if the disruption is still there.
Far Field Monitor - another antenna at the threshold end of the runway pointing at the loc. Only applicable to Cat II/III systems (I think still). More monitoring, more grumpiness if the signal is disrupted.
More boring information . . . . ILS is run on battery power with the lead acid batteries being constantly charged from the mains. This ensures that in the event of a power failure at least the one on the approach can land. For Cat II/III systems, during LVP, power is provided from a generator with the mains supply being the back up. This ensures the required less than one second break in the event of a failure. You don't arf get through a lot of gas oil when in constant LVP . . . .