Date: 202105
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach; Initial Approach
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Human-Machine Interface; Troubleshooting
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Ground Equipment Issue; Inflight Event / Encounter CFTT / CFIT
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem
Contributing factors: ATC Equipment / Nav Facility / Buildings; Procedure; Human Factors
Primary problem: Human Factors

Narrative: After intercepting the glideslope it was noted by both pilots the aircraft was not slowing down normally.  Despite lowering the gear and deploying speedbrakes we were having a difficult time getting 10 knots below the next flap speed to continue to configure a variable tailwind was noted between 5 & 10 knots which helped explain what we were seeing.  Continuing to investigate however both pilots thereafter realized we were abnormally low and the PF disconnected the AP and leveled off.  Tower called with a low altitude alert shortly after that and we acknowledged it; configured normally and were stable by 500 feet AGL.  Landing and roll out was normal.  There were multiple approach NOTAMs that day and we miscalculated the effective times on the one stating the ILS XXL was unusable.  We were an hour off and were arriving inside the last 30 minutes of the effective time.  It turns out NAVAIDs maintenance was manipulating the glide slope signal at the time; causing the glide slope to appear lower.The ILS to XXL was OTS and NAVAIDs maintenance was transmitting a lower than normal glidepath. It would have been helpful if ILS status had been repeated on the ATIS; as it normally is; but it was not.  During the low altitude call from tower they were even quick to add to the call that it 'was in the NOTAMs'.  Further investigating with my prior position with FAA Flight Inspection it is still in their guidance that NAVAIDs maintenance is not supposed to transmit a localizer signal if they are going to manipulate the glide slope signal to avoid this hazardous; misleading; information.  The localizer and glide slope both were transmitting; with a proper ID; at the time of the incident; we even crossed ZZZZZ at the appropriate altitude of 3;000 and showed on path.  It was after that when the aircraft would no longer slow; as it was chasing a depressed glide path.  In the end we missed the NOTAM but then multiple holes of the swiss cheese lined up; thankfully it was day VFR and we saw the solution with our own eyes in time.  The other layers of protection normally there (ATIS; maintenance procedures) would have helped overcome our oversight.




Synopsis: A320 First Officer reported CFIT event during approach that was due to maintenance before performed on the glide slope equipment but not being announced on ATIS.