Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 220; Flight Crew Total 14000; Flight Crew Type 11000
Other / Unknown
No Specific Anomaly Occurred All Types
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings
This is the third write up for this particular issue. I have seen this issue almost consistently over the last nine years. The glide slope for ILS Runway 10 at BWI oscillates up and down. It is very noticeable very far out (more than 20 miles). As you get closer the total deviation is smaller (approximately one 'dot' amplitude cycle every one second at around 12 miles). However; even lined up with the localizer; the deviations are still apparent and the flight director's command nose up and down movements in sync with the glide path. Had we had the autopilot on; it would have moved the nose up and down and probably would have kicked the autopilot off. It's as if there is a harmonic effect from interference; or an installation problem; or maybe something emitting near the airport that affects the glide slope. My big concern is that this approach is the only CAT II/III approach at BWI; and is frankly unusable as a CAT I ILS. I certainly don't trust it. BWI used Runway 33L ILS approaches the vast majority of the time.
Air Carrier landing BWI experienced glideslope oscillations while on the ILS Runway 10 approach.  The reporter noted this anomaly had been experienced on a number of other occasions.