Narrative:

I was working controller in charge and a PA42 was inbound for runway 30R. After checking on frequency; a low altitude (la) alert began sounding and the approach controller immediately called on the shout line to advise us of the alert. As soon as I heard the alert; I verbally reminded local control (local control) to issue the alert and answered the shout line to acknowledge; while local control issued the alert. There was no response from the aircraft; and I immediately told local control to issue it again. Still no response; and local control called the aircraft again. At this point; the aircraft finally responded and acknowledged they were correcting back onto the approach course (they were low and south of the ILS course at that point). The aircraft appeared to continue inbound to the airport; but looked much higher than normal on the final (above 070; if I recall). It certainly did not look like they were established the glideslope; but I was glad they at least had some altitude at this point. When it appeared the PA42 was near a 1 mile final; I heard them say they 'had visual' and I looked to try to acquire the aircraft. Finally; I spotted the aircraft north of the final at a low altitude; almost where I might expect to see someone on a tight right base turning towards the final. The PA42 then landed safely. Later in the hour; an arriving aircraft on the approach reported the localizer appeared to not be functioning normally. After that report; the PA42 called to taxi out for departure and ground control asked the crew if they recalled having a problem with the localizer. The pilot said they believed there was a problem with their autopilot instead while they flew the approach. Additional pilot reports from subsequent arrivals indicated that the localizer appeared to be working normally. I am not sure whether the arrival's strange approach was caused by autopilot or localizer issues; or something entirely different. This event revealed to me of an area of concern; which is ensuring we avoid complacency when it comes to issuing safety alerts; particularly low altitude alerts. It is not uncommon to encounter 'nuisance alerts' when it's VMC for days or weeks; often from IFR aircraft on visual approaches. Normally the alarm goes off; but the aircraft is clearly visible out the window and the controller determines it is not in an unsafe position that would justify issuing an alert to the pilot. I believe there have been many efforts to mitigate the number of nuisance alerts we get; with much success in the last few years. However; as soon as it goes IMC: *completely* different scenario and virtually any la alarm heard is legit. If that low altitude alert goes off or the aircraft is observed in a abnormal position; there should be no delay in issuing that prescribed phraseology to the pilot - and if there is no acknowledgement; immediately issuing the alert again. I am concerned that we may not issue these alerts often enough to be proficient at using complete; correct phraseology when that alarm sounds. I found learning the phraseology tricky; since the transmission should begin with 'low altitude alert'; as opposed to starting with the callsign as we're accustomed. A personal technique I developed to try to combat complacency is rehearsing la phraseology in my head; just prior to taking the position during IMC. I find envisioning the steps I would take to handle an alert is personally very effective in recalling the phraseology and feeling empowered to immediately issue it when the situation calls.

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Original NASA ASRS Text

Title: BJC CIC describes a low altitude alert issued to a PA42 on the ILS to Runway 30R. Several calls are required to get the pilot to respond and climb to a more appropriate altitude.

Narrative: I was working CIC and a PA42 was inbound for Runway 30R. After checking on frequency; a Low Altitude (LA) Alert began sounding and the approach controller immediately called on the shout line to advise us of the alert. As soon as I heard the alert; I verbally reminded Local Control (LC) to issue the alert and answered the shout line to acknowledge; while LC issued the alert. There was no response from the aircraft; and I immediately told LC to issue it again. Still no response; and LC called the aircraft again. At this point; the aircraft finally responded and acknowledged they were correcting back onto the approach course (they were low and south of the ILS course at that point). The aircraft appeared to continue inbound to the airport; but looked much higher than normal on the final (above 070; if I recall). It certainly did not look like they were established the glideslope; but I was glad they at least had some altitude at this point. When it appeared the PA42 was near a 1 mile final; I heard them say they 'had visual' and I looked to try to acquire the aircraft. Finally; I spotted the aircraft north of the final at a low altitude; almost where I might expect to see someone on a tight right base turning towards the final. The PA42 then landed safely. Later in the hour; an arriving aircraft on the approach reported the localizer appeared to not be functioning normally. After that report; the PA42 called to taxi out for departure and Ground Control asked the crew if they recalled having a problem with the localizer. The pilot said they believed there was a problem with their autopilot instead while they flew the approach. Additional pilot reports from subsequent arrivals indicated that the localizer appeared to be working normally. I am not sure whether the arrival's strange approach was caused by autopilot or localizer issues; or something entirely different. This event revealed to me of an area of concern; which is ensuring we avoid complacency when it comes to issuing Safety Alerts; particularly Low Altitude Alerts. It is not uncommon to encounter 'nuisance alerts' when it's VMC for days or weeks; often from IFR aircraft on visual approaches. Normally the alarm goes off; but the aircraft is clearly visible out the window and the controller determines it is not in an unsafe position that would justify issuing an alert to the pilot. I believe there have been many efforts to mitigate the number of nuisance alerts we get; with much success in the last few years. However; as soon as it goes IMC: *completely* different scenario and virtually any LA alarm heard is legit. If that Low Altitude Alert goes off or the aircraft is observed in a abnormal position; there should be no delay in issuing that prescribed phraseology to the pilot - and if there is no acknowledgement; immediately issuing the alert again. I am concerned that we may not issue these alerts often enough to be proficient at using complete; correct phraseology when that alarm sounds. I found learning the phraseology tricky; since the transmission should begin with 'LOW ALTITUDE ALERT'; as opposed to starting with the callsign as we're accustomed. A personal technique I developed to try to combat complacency is rehearsing LA phraseology in my head; just prior to taking the position during IMC. I find envisioning the steps I would take to handle an alert is personally very effective in recalling the phraseology and feeling empowered to immediately issue it when the situation calls.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.