Date: 201403
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Haze / Smoke; Turbulence; 7
Light: Night
Aircraft: Cessna 210 Centurion / Turbo Centurion 210C; 210D
Operator: FBO
Operating under: Part 91
Flight plan: IFR
Mission: Training
Flight phase: Final Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: ILS/VOR
Component problem: Improperly Operated
Reporter organization: FBO
Reporter function: Instructor; Pilot Not Flying
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor
Human factors: Distraction; Troubleshooting; Training / Qualification; Situational Awareness; Human-Machine Interface; Confusion
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Automation Air Traffic Control; Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors; Procedure; Weather
Primary problem: Human Factors

Narrative: I was the CFII on this flight for an instrument rated commercial student of mine. What happened: Glideslope came alive on ILS; and got STUCK. While my student thought she was flying a perfect glideslope; we were on a collision course for the ground. Background info: This flight was the 300 NM cross country flight required for the commercial rating. We were on our way back to our home base. I am a newly minted CFII. 600 hours TT. I have 100+ hour of actual instrument time from flying a G1000 C208. While I have 40+ hours in the C210 we were flying; I've flown only one or two approaches in it. Similarly; my student had 10+ hours in the airplane; but little recent instrument time. While we both were inclined to scrub the flight and try and come home the next day; it was Spring Break in Key West; and there was NO place left to stay overnight; so we decided to fly home. Though my student lacked much current instrument experience; I was confident in my ability to shoot the ILS. Well; I'm letting my student fly the ILS. We turned inbound... glideslope came alive and moved to 'one dot high.' Student started descending; fast. VSI and altimeter were decreasing. By the time the altimeter reached 600 FT I knew something was wrong. Luckily I had the GPS procedure loaded as well; so I could see our distance from the MAP was still 2+ miles. I grabbed the controls; leveled off. Less than 2 seconds later Tower comes on the radio and tells us they're getting an altitude alert. I leveled off; kept flying; and sure enough the glideslope stayed pegged right where it was; indicating one dot high. I just kept my altitude (600 MSL) because I knew it was above the LOC minimums (480 MSL) and 1 MI from the missed approach point I was about to go around when my student caught the MASLRS. Conclusion: I am thoroughly convinced that almost anyone in this situation could have flown themselves into the ground following a false glideslope indication. For me; typically flying ILS approaches on glass avionics; the idea of the glideslope indicator getting stuck was totally foreign to me. Thankfully I was able to recognize things were not right; but I don't think everyone might have been that lucky. If my student was alone and the ILS was unmonitored; they could have ended up in the trees.

Callback: Reporter stated the airport's ILS glideslope was reported out of service earlier in the day but reported functional at the time of this approach. After landing and turning the aircraft over to maintenance it was determined that the aircraft's ILS receiver was functional so the crew realized fully what had happened.



Synopsis: Flying a G1000 equipped C210; an instructor and commercial student pilot flew a night IMC ILS to the their home base and descended to 600 FT on a false glideslope. ATC called a low altitude alert concurrent with the instructor identifying the condition on his backup GPS.