|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Make Model Name||B737 Undifferentiated or Other Model|
|Operating Under FAR Part||Part 121|
|Route In Use||Other Instrument Precision|
Pilot Not Flying
|Experience||Flight Crew Last 90 Days 150|
Flight Crew Type 150
|Anomaly||Deviation - Procedural Published Material / Policy|
Inflight Event / Encounter Loss Of Aircraft Control
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.