The flight crew of a C-680 twice executed missed approaches on the ILS 19L (GS out) approach to TEB due to low altitude alerts and EGPWS warnings. Inconsistent ATC terminology as to the functionality of the GS and the presence of a tower higher than the (GS out) DH on short final contributed to the event. The flight diverted successfully following the second missed approach.
Synopsis
The flight crew of a C-680 twice executed missed approaches on the ILS 19L (GS out) approach to TEB due to low altitude alerts and EGPWS warnings. Inconsistent ATC terminology as to the functionality of the GS and the presence of a tower higher than the (GS out) DH on short final contributed to the event. The flight diverted successfully following the second missed approach.
Narrative
The weather at TEB was 300 FT overcast and 1-1/2 miles visibility. The approach in use was the ILS to Runway 19. The NOTAMS for Runway 19 said that due to effects of the amount of snow the ILS minimums (300/1) were raised to the LOC minimums (580/1). The NOTAM also said that the GS remained in service but the angle might be different than published. The ATIS said that the GS was unreliable and New York Approach said the GS was unusable. Since New York Approach used the term unusable and we had the visibility for the approach we elected to fly the approach using the profile for a LOC only approach.As we passed the FAF; I (non-flying pilot) contacted Tower and the pilot flying started a 1000 FPM descent to the LOC MDA. We both noted that the GS indicator showed use below the GS (as you would expect on a LOC only approach). Shortly after that we got a call from Tower giving us a low altitude alert and check our altimeters. We checked the altimeters and the PF climbed back to the GS. We continued; on the GS; to the LOC MDA and to the MAP. Nothing was in sight and we executed a missed approach to a second try. On the second approach the pilot flying flew the same profile and at the same point we got an EGPWS warning and the low altitude alert from Tower. We executed a missed approach and proceeded to our alternate for an uneventful landing. We could not understand why we were getting the altitude warnings as we were above the LOC MDA when we got both warnings.After landing we examined the approach and saw a tower 694 FT high to the right of the course about 2.0 miles from the end of the runway. We followed our training in that when we heard the GS was unusable we flew a LOC only approach profile. It appears that ATC's intent was to have us fly the ILS approach; using the GS; but down to the LOC minimums. The information we were given (NOTAMS; ATIS; Approach) was conflicting.Finally; if the GS is really out there should be a step down fix published for the approach to Runway 19 at TEB.
NASA callback
The reporter noted the problem with GS signals was widespread throughout the New York area; apparently because of conflicts between the GS antennae and the high levels of snow buildup. He emphasized he believed the underlying cause of the events to be poor and/or inconsistent terminology from different ATC sources with respect to the status of the GS. He accepted responsibility for not having clarified the intended constraints on its use and what was expected with respect to conducting the approach; particularly before the second attempt. He does not recall the phraseology used when he was cleared for the approach; i.e.; whether the controller stated 'GS out of service' when doing so. He did state that; as the pilot not flying; he was deeply engaged in planning for diversion operations while the pilot flying concentrated on flying. Workload and fuel concerns contributed to their ability to process all the factors.He continues to question how; if necessary; an EGPWS equipped aircraft could fly a 'classic' non-precision 'dive and drive' approach without triggering a terrain warning with respect to the tower (some 120 FT higher than the MDA) located only ~ 6/10s of a mile from the centerline and ~1.2 miles from the end of the runway. He reiterated the second approach was a classic 'dive and drive' which was not (and could not have been) completed because of the terrain warning and the pull up the warning mandates.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.