Commuter executing ILS to 16R at sea experiences erratic glideslope reception.

Attributes
ACN	132242
Time
Date	198912
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sea
State Reference	WA
Altitude	agl bound lower : 0 agl bound upper : 1000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : sea
Operator	common carrier : air taxi
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 210 flight time total : 1938
ASRS Report	132242
Person 2
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

On approach to runway 16R at sea, the G/south indicator scalloped +/- 1 DOT on both the captain's and first officer's indicators. The WX was reported at 200' overcast, the RVR was 2200'. Just as the captain called the approach lights and runway in sight, the G/south indicator jumped, showing 2 dots above the G/south. By then we were in visibility contact with the runway and the first officer executed a normal landing. As we touched down, I noticed an large transport, which had executed the ILS in front of us, just crossing the parallel runway (16L). It is my opinion that the large transport, due to reduced sep, interfered with the G/south signal which we were receiving. The G/south receiver in the airplane worked normally subsequently while on an ILS approach into geg.

Original NASA ASRS Text

Title: COMMUTER EXECUTING ILS TO 16R AT SEA EXPERIENCES ERRATIC GLIDESLOPE RECEPTION.

Narrative: ON APCH TO RWY 16R AT SEA, THE G/S INDICATOR SCALLOPED +/- 1 DOT ON BOTH THE CAPT'S AND F/O'S INDICATORS. THE WX WAS RPTED AT 200' OVCST, THE RVR WAS 2200'. JUST AS THE CAPT CALLED THE APCH LIGHTS AND RWY IN SIGHT, THE G/S INDICATOR JUMPED, SHOWING 2 DOTS ABOVE THE G/S. BY THEN WE WERE IN VIS CONTACT WITH THE RWY AND THE F/O EXECUTED A NORMAL LNDG. AS WE TOUCHED DOWN, I NOTICED AN LGT, WHICH HAD EXECUTED THE ILS IN FRONT OF US, JUST XING THE PARALLEL RWY (16L). IT IS MY OPINION THAT THE LGT, DUE TO REDUCED SEP, INTERFERED WITH THE G/S SIGNAL WHICH WE WERE RECEIVING. THE G/S RECEIVER IN THE AIRPLANE WORKED NORMALLY SUBSEQUENTLY WHILE ON AN ILS APCH INTO GEG.

Data retrieved from NASA's ASRS site as of August 2007 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.