An air carrier pilot reports his aircraft pitching in response to glideslope and localizer fluctuati...

Narrative:

After being cleared for an ILS approach to runway 16L and just before the FAF glide slope deviations of more than 2 dots down was encountered with aircraft autopilot pitching down to follow glide slope. Autopilot was disconnected and approach was continued. We were somewhat ready for this event since the company aircraft ahead of us complained of the same thing happening to them. Once on tower frequency; I asked if an aircraft had just crossed the centerline of runway 16L and they replied that the critical area was not protected. I am hoping that this report will be added to the growing complaints generated by this less than acceptable NAVAID performance as it stands now. Protect the ILS critical area any time an aircraft is cleared for an ILS to runway 16L. Better yet; relocate the glide slope antenna so these dangerous deviations won't occur.

Original NASA ASRS Text

Title: AN AIR CARRIER PILOT REPORTS HIS AIRCRAFT PITCHING IN RESPONSE TO GLIDESLOPE AND LOCALIZER FLUCTUATIONS AT 3;300 FT WHILE FLYING A COUPLED ILS TO SEA RUNWAY 16L.

Narrative: AFTER BEING CLEARED FOR AN ILS APPROACH TO RUNWAY 16L AND JUST BEFORE THE FAF GLIDE SLOPE DEVIATIONS OF MORE THAN 2 DOTS DOWN WAS ENCOUNTERED WITH AIRCRAFT AUTOPILOT PITCHING DOWN TO FOLLOW GLIDE SLOPE. AUTOPILOT WAS DISCONNECTED AND APPROACH WAS CONTINUED. WE WERE SOMEWHAT READY FOR THIS EVENT SINCE THE COMPANY AIRCRAFT AHEAD OF US COMPLAINED OF THE SAME THING HAPPENING TO THEM. ONCE ON TOWER FREQUENCY; I ASKED IF AN AIRCRAFT HAD JUST CROSSED THE CENTERLINE OF RUNWAY 16L AND THEY REPLIED THAT THE CRITICAL AREA WAS NOT PROTECTED. I AM HOPING THAT THIS REPORT WILL BE ADDED TO THE GROWING COMPLAINTS GENERATED BY THIS LESS THAN ACCEPTABLE NAVAID PERFORMANCE AS IT STANDS NOW. PROTECT THE ILS CRITICAL AREA ANY TIME AN AIRCRAFT IS CLEARED FOR AN ILS TO RUNWAY 16L. BETTER YET; RELOCATE THE GLIDE SLOPE ANTENNA SO THESE DANGEROUS DEVIATIONS WON'T OCCUR.

Data retrieved from NASA's ASRS site as of April 2012 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	818411
Time
Date	200901
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Route In Use	Other Instrument Precision
Flight Plan	IFR
Person 1
Function	Captain Pilot Not Flying
Experience	Flight Crew Last 90 Days 150 Flight Crew Type 150
Events
Anomaly	Deviation - Procedural Published Material / Policy Inflight Event / Encounter Loss Of Aircraft Control

An air carrier pilot reports his aircraft pitching in response to glideslope and localizer fluctuations at 3;300 ft while flying a coupled ILS to sea runway 16L.