Date: 201901
Local time of day: 1801-2400
Location: ORD.Airport, IL
Flight conditions: IMC
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ORD
ATC / advisory: TRACON C90
Second aircraft: Commercial Fixed Wing
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Communication Breakdown
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: ATC Equipment / Nav Facility / Buildings; Weather
Primary problem: ATC Equipment / Nav Facility / Buildings

Narrative: I was working West Arrival; vectoring aircraft for the ILS to RWY 28C at ORD. There was adverse winter weather in the area at this time; restricting ORD to a 2 runway arrival operation. Due to this; demand was high; and constant. All day; the RWY 28R glideslope had been out (presumed due to weather issues). During a busy period of traffic; the city wanted to have RWY28C groomed; cleaned and inspected due to the continuing ice conditions. At this point; 28R glideslope was returned to service. I was informed by the main arrival coordinator to begin vectoring arrivals to the new runway; and told the [glideslope] would be fully functional. I made the challenging switch to the new runway; and immediately had a full final to about 40 NM. I noticed the low altitude alert go off for Aircraft X; and issued the warning. Aircraft X arrested their descent; and noted they were having an issue with the glideslope. At this point I noticed Aircraft Y that was also descending well below the glideslope. I immediately climbed them; and issued missed approach instructions. From this point; it was obvious there was still an issue with the glideslope; so I went ahead with the arduous task of reissuing every aircraft the localizer approach for runway 28R. This; along with what was already a busy airspace full of airplanes; Aircraft X and Aircraft Y both then needed to go around for unstable approaches. I was unable to make the coordination with the tower as I was too busy managing my aircraft. At this point the glideslope was taken out of service and deemed unreliable. This caused several ATIS changes; to reflect the equipment malfunction; and approach changes. Along with the rapidly changing weather; I again was oversaturated giving the new ATIS and weather conditions to pilots. It seems the appropriate work wasn't completed to remedy the problem on the glideslope; and nearly caused Aircraft X and Aircraft Y to descend below the MVA (Minimum Vectoring Altitude) as they crossed Downtown Chicago in IFR conditions. This seems like a serious safety issue. Have some better form of verification equipment is working prior to resuming using that equipment.




Synopsis: Chicago TRACON Controller reported adverse weather and a malfunctioning glideslope caused aircraft to go around.