Flight crew reported ATC failed to issue the proper approach resulting in receiving erroneous glide slope references; low altitude alert and incorrect crossing altitude.
Synopsis
Flight crew reported ATC failed to issue the proper approach resulting in receiving erroneous glide slope references; low altitude alert and incorrect crossing altitude.
Narrative
Returning from ZZZZ; expecting and set up for ILS 30. MIA in west ops for winds which were out of the north approximately 20-25 kts with higher gusts. Approach told us to expect ILS 27. I was Pilot Flying (PF). Pilot Monitoring (PM) set up ILS 27. Set up and briefed flaps 15 landing. Vectored by approached to intercept LOC while descending to intercept glidepath. Cleared for the approach and switched to Tower. We intercepted glideslope before LOC. Everything looked good until FAF when tower called us with an altitude alert. We were on glideslope but 250-300 low. PM called out ground contact (we were IMC) and position clear of buildings. We continued approach but several times the glideslope indications went both up and down quickly (as if an aircraft was taxiing past the transmitter). Broke out several hundred feet above mins and continued to landing. After landing PM called tower to inform them of the issues on the ILS. Tower responded that there were issues with the ILS and we should have been given the RNAV approach. Double checked the ATIS and it was showing ILS 27 available.Cause: Miss communication between tower and approach controller(s).Suggestions: Better; more timely; communication between controlling agencies.
Second reporter narrative
Captain flying ILS to 27. Just past CHHAZ tower called out Low Altitude Alert for us. We showed on glide path. I referenced the approach and saw CHHAZ should be at 1;800 ft. We were just above 1;500 ft. showing on glide path. Something not correct obviously; I stated ground contact looking down at the shoreline. I could see forward and the ground just in front of the aircraft; but no approach lights yet. The glideslope then abruptly jumped up and then down and then something close to on glideslope. Just like you get when someone crosses the glideslope signal flying the ILS Runway 30. The ILS signal was steady after that. The Captain continued while I leaned forward and maintained visual with the ground just in front of the aircraft. At about 700-800 ft. AGL I called the approach lights in sight. Captain landed uneventfully. As we cleared I told the tower there was something wrong with the glideslope. Tower stated that had been reported and we should have been on the RNAV. Approach was still clearing aircraft for the ILS however.Cause: With a known problem with the glideslope; the ILS glideslope should have been turned off. Approach control should not have been clearing aircraft to fly it.Suggestions: The tower altitude alerting feature works well. We both missed the FAF crossing altitude check and were tracking the steady glideslope signal. The tower alert followed seconds later by a 3-5 second spurious signal certainly got our attention. Without the tower alert we may have never realized we must have crossed the FAF probably 150 ft. -250 ft. low showing on glideslope.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.