The bwi ILS runway 10 glide slope oscillated up and down one half a dot between 2000 and 1500 ft whe...

Attributes
ACN	825383
Time
Date	200902
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Other Instrument Precision
Flight Plan	IFR
Person 1
Function	Pilot Not Flying
Experience	Flight Crew Last 90 Days 200 Flight Crew Total 8000 Flight Crew Type 6000
Events
Anomaly	Other ILS Glide Slope

Narrative:

Third time this month on ILS runway 10 at bwi. Intercepting from left of course at 8 miles from td this time; below glide path by one to zero dots; between 2000 and 1500 ft. Glide path oscillated +/- half a dot consistently (approximately one cycle per second?) until well inside FAF; then slowly stabilizes. At about 200 ft to about 50 ft; gp oscillates about twice as fast; but with less magnitude; decreasing to negligible but higher freq/less magnitude. Previously wrote this up at least one to two years ago. Saw this three separate times in feb/09 as PF and PNF. Resembles an interference issue/harmonics?

Original NASA ASRS Text

Title: The BWI ILS Runway 10 glide slope oscillated up and down one half a dot between 2000 and 1500 ft when a B757 intercepted the localizer the left. Oscillations continued inside of the FAF but the amplitude decreased down to about 50 ft.

Narrative: Third time this month on ILS Runway 10 at BWI. Intercepting from left of course at 8 miles from TD this time; below glide path by one to zero dots; between 2000 and 1500 ft. Glide path oscillated +/- half a dot consistently (approximately one cycle per second?) until well inside FAF; then slowly stabilizes. At about 200 ft to about 50 ft; GP oscillates about twice as fast; but with less magnitude; decreasing to negligible but higher freq/less magnitude. Previously wrote this up at least one to two years ago. Saw this three separate times in Feb/09 as PF and PNF. Resembles an interference issue/harmonics?

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.

The bwi ILS runway 10 glide slope oscillated up and down one half a dot between 2000 and 1500 ft when a B757 intercepted the localizer the left. Oscillations continued inside of the FAF but the amplitude decreased down to about 50 ft.