Date: 201910
Local time of day: 0601-1200
Location: ELM.Airport, NY
Flight conditions: VMC
Aircraft: Light Transport
Operator: Air Taxi
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class D ELM
ATC / advisory: TRACON ELM
Reporter organization: Air Taxi
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Second reporter function: First Officer; Pilot Not Flying
Anomaly: ATC Issue All Types; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Executed Go Around / Missed Approach
Contributing factors: ATC Equipment / Nav Facility / Buildings
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: Low altitude alert by ATC. GS (Glide Slope) was stuck centered. While flying a normal IFR approach using a flight director; the approach was proceeding normally on profile; received a low altitude alert; compared left to right; and went missed. The GS on the left side HSI and FD (Flight Director) stayed frozen in the center during the climb. The GS returned to normal operation when the lights were turned off as part of the cleanup on the climb. First Officer said he was about make a call about a disagreement with his GS to mine. ATC stated they had GS equipment issues the day before; and wanted to know the outcome of us tuning in the VS/ILS in ZZZ after the VFR landing.Apparently an equipment failure; either with the GS or receiver.Compared GS indication; went missed; Diversion to ZZZ to land VMC; tested GS on a VMC approach; nothing abnormal noted.A repeater NAV#2 with a GS like on many planes; visible from the left side would allowed the Captain to compare GS on the approach. Had this occurred without a Copilot or at an uncontrolled airport; the result would have been a crash with no GPWS (Ground Proximity Warning System). The fact that the local VOR/DME has been removed from service greatly limits your ability to fix you position when the flying the approach without a GPS.


Second narrative: We were on approach for the ILS Runway 24 in to ELM when we noticed a disagreement between the Captain's glideslope and the First Officer's glideslope. The glideslope on the Captain's flight director and HSI were showing centered; however; the First Officer's glideslope was showing about 2 dots low. We received a low altitude alert and subsequently went missed. ZZZ was reporting VFR conditions and we diverted there. We did the visual approach to Runway 16 at ZZZ backed up by the ILS Runway 16 to test both sets of flight instruments. Both the Captain's and First Officer' glideslope indicators were showing correct and matching. The Captain called the Chief Pilot; as well as Dispatch and Maintenance Control; to help determine the best course of action. [Company] picked up the cargo at ZZZ and then we waited for the weather to improve at ELM; so we could do the re-position flight to ELM VFR. The controller at ELM reported that they were having some issues with the ILS system yesterday.When the First Officer's instruments were cross checked with the Captain's instruments; and with the low altitude alert from the controller at ELM.Both of the glideslope indicators on the flight director and HSI on the Captain's flight instruments were stuck and indicating on glidepath. I am not sure if it is an issue with the receiver or possibly something wrong with the ILS system at ELM.Immediately going around to troubleshoot the issue; maintaining VFR conditions and landing VFR at ZZZ.I think having a GPS (Global Positioning System) in the aircraft with the approach loaded up would have increased the situational awareness; and we would have been able to easily see when we were passing each fix and what altitude we should be at. The ELM VOR is permanently out of service so you cannot easily identify each fix on the approach with DME.


Synopsis: Light Transport flight crew reported a glideslope failure on approach to ELM airport that resulted in a diversion.