Narrative:

On the ILS V 9R approach in phl; we were cleared for the approach at 2;000 until established; 170 knots to kelee. Inside asoci we descended to 1;800 to capture the GS. Aircraft was configured for landing at the FAF. As checklist was being completed; the first officer (first officer) indicated an anomaly with the approach; that something was wrong. The GS indicator was not showing and the plane was descending. The autopilot was disconnected and I called for and initiated a go-around; taking control of aircraft. As the go-around commenced; ATC advised of a low altitude alert. The go-around was executed and completed as ATC issued a clearance to climb to 3;000 feet and vectors to the southwest. ATC then asked if we wanted to try the ILS V runway 17 due to the more favorable winds for that runway and the possible glideslope issue on 9R. We accepted vectors for the ILS V runway 17 and flew a standard approach to a landing; with all aircraft autoflight systems operating normally. The first officer resumed control of the aircraft after the go around was completed and flew the subsequent approach to landing. Flight crew awareness that aircraft was descending on a path outside the normal glideslope path for the approach. Not certain why event occurred. It appears the autopilot descended the aircraft on a path other than the intended glideslope for the approach. Possible glideslope failure. Not sure what anomaly occurred; but it appeared to be a one-time event as the aircraft systems operated normally for the subsequent approach. Crew situational awareness and CRM contributed to successfully recognizing the unintended flight path and discontinuing the approach; executing a go around.

Related reports:

Google
 

Original NASA ASRS Text

Title: A Turboprop Captain reports getting below the glideslope during a night visual approach to PHL with the First Officer flying. The First Officer indicates that something is amiss with the approach and the Captain takes control and executes a go-around at the same time the Tower issues a low altitude alert.

Narrative: On the ILS V 9R Approach in PHL; we were cleared for the approach at 2;000 until established; 170 knots to KELEE. Inside ASOCI we descended to 1;800 to capture the GS. Aircraft was configured for landing at the FAF. As checklist was being completed; the First Officer (FO) indicated an anomaly with the approach; that something was wrong. The GS indicator was not showing and the plane was descending. The autopilot was disconnected and I called for and initiated a go-around; taking control of aircraft. As the go-around commenced; ATC advised of a low altitude alert. The go-around was executed and completed as ATC issued a clearance to climb to 3;000 feet and vectors to the southwest. ATC then asked if we wanted to try the ILS V Runway 17 due to the more favorable winds for that runway and the possible glideslope issue on 9R. We accepted vectors for the ILS V Runway 17 and flew a standard approach to a landing; with all aircraft autoflight systems operating normally. The FO resumed control of the aircraft after the go around was completed and flew the subsequent approach to landing. Flight crew awareness that aircraft was descending on a path outside the normal glideslope path for the approach. Not certain why event occurred. It appears the autopilot descended the aircraft on a path other than the intended glideslope for the approach. Possible glideslope failure. Not sure what anomaly occurred; but it appeared to be a one-time event as the aircraft systems operated normally for the subsequent approach. Crew situational awareness and CRM contributed to successfully recognizing the unintended flight path and discontinuing the approach; executing a go around.

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.