Oak tower controller describes situation with an aircraft on final that loses ILS signal due to the ...

Narrative:

I was working LC1 at night and we had low ceilings. It was about BKN006 and we were protecting for the ILS critical area. Aircraft X was cleared to land on about a 7 mile final and I put aircraft Y in position. I then noticed that aircraft X was starting to drift north of course on the ILS approach. He was about a quarter mile north of course; but still paralleling the ILS approach course. I gave him about half a mile to see if he would correct his course. He did not; so I told him he appeared north of course; and to verify correcting. The pilot said yeah we're correcting now; and something about there being a momentary outage. He asked if there was someone in the way of the signal. I said that aircraft Y was going into position. By the time the conversation was over; aircraft X corrected course and it seemed the signal was normal. The problem here is that our runway was shortened due to rsa work and the landing threshold was moved. The ILS course was also moved to reflect the new end of the runway; but management never provided us information about where the new instrument shacks were on the airport and where the critical areas were. The only maps we have to reference are for when the runway used to be full length. So when we have to protect the critical area due to low ceilings; no one has any idea where the critical areas are and we have no map to reference.I believe that when the big aircraft Y taxied into position on the runway; he must have went right through the critical area and since he was so slow in doing so; must have blocked the signal. Luckily aircraft X was still far enough out on final that the pilot was able to correct and there wasn't a go around with two aircraft up in the clouds where no one can see them.we need to know where the new instrument shacks are and where the ILS critical areas are. Vehicles call us all the time asking to cross the approach on the access road; but we don't truly know if the access road goes into any ILS critical areas either.

Original NASA ASRS Text

Title: OAK Tower Controller describes situation with an aircraft on final that loses ILS signal due to the Controller taxiing a heavy aircraft into position. Facility has not provided controllers with critical areas to protect.

Narrative: I was working LC1 at night and we had low ceilings. It was about BKN006 and we were protecting for the ILS critical area. Aircraft X was cleared to land on about a 7 mile final and I put Aircraft Y in position. I then noticed that Aircraft X was starting to drift north of course on the ILS approach. He was about a quarter mile north of course; but still paralleling the ILS approach course. I gave him about half a mile to see if he would correct his course. He did not; so I told him he appeared north of course; and to verify correcting. The pilot said yeah we're correcting now; and something about there being a momentary outage. He asked if there was someone in the way of the signal. I said that Aircraft Y was going into position. By the time the conversation was over; Aircraft X corrected course and it seemed the signal was normal. The problem here is that our runway was shortened due to RSA work and the landing threshold was moved. The ILS course was also moved to reflect the new end of the runway; but Management never provided us information about where the new instrument shacks were on the airport and where the critical areas were. The only maps we have to reference are for when the runway used to be full length. So when we have to protect the critical area due to low ceilings; no one has any idea where the critical areas are and we have no map to reference.I believe that when the big Aircraft Y taxied into position on the runway; he must have went right through the critical area and since he was so slow in doing so; must have blocked the signal. Luckily Aircraft X was still far enough out on final that the pilot was able to correct and there wasn't a go around with two aircraft up in the clouds where no one can see them.We need to know where the new instrument shacks are and where the ILS critical areas are. Vehicles call us all the time asking to cross the approach on the access road; but we don't truly know if the access road goes into any ILS critical areas either.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1182918
Time
Date	201406
Local Time Of Day	1201-1800
Place
Locale Reference	OAK.Airport
State Reference	CA
Environment
Light	Night
Aircraft 1
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Other Instrument Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Widebody Low Wing 3 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Route In Use	None
Flight Plan	IFR
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 2.6
Events
Anomaly	ATC Issue All Types Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy

Oak tower controller describes situation with an aircraft on final that loses ILS signal due to the controller taxiing a heavy aircraft into position. Facility has not provided controllers with critical areas to protect.