Narrative:

We were assigned and flying the new york jfk VOR DME runway 22L approach using the FMS in LNAV and VNAV on the autoplt to minimums. After descending below the minimums of 440 ft MSL; as we descended through 300 ft MSL; the VNAV function malfunctioned. The flight director slowly commanded a leveloff and the vdi slowly showed the need to level off. The approach on the FMS showed a 3.14 degree GS all the way to the runway. My first officer stated that this phenomenon is observed all the time on runway 22L at jfk. Since we can now go below MDA without seeing the PAPI this is a real problem here at jfk. Since the problem is computer generated by the airplane it is not something that the airport at jfk has done. It's very disconcerting to be shown inaccurate GS information below MDA. In worst case a crew would lose GS information below 300 ft and not be able to see the PAPI either. Callback conversation with reporter revealed the following information: reporter amended his narrative to indicate that descent below the MDA is authorized with approach light components in view. The comment regarding the PAPI was misleading in this regard. Reporter's concern is that; unlike the air carrier's training exercise -- which was a straight-in approach with continued GS guidance until touchdown -- this approach eliminates the GS guidance at the map and continued descent below MDA must be accomplished with no glide path monitor available. The situation has been discussed with the air carrier flight training department without a satisfactory resolution of the reporter's concerns. Reporter has suggested that training should include both the straight-in scenario and the one that exists at jfk. He feels descent below the MDA at jfk should not be authorized due to the lack of glide path guidance.

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Original NASA ASRS Text

Title: B777 ON VOR 22L APCH TO JFK UTILIZING FMS GENERATED GS LOSES GS INDICATIONS BELOW MDA.

Narrative: WE WERE ASSIGNED AND FLYING THE NEW YORK JFK VOR DME RWY 22L APCH USING THE FMS IN LNAV AND VNAV ON THE AUTOPLT TO MINIMUMS. AFTER DSNDING BELOW THE MINIMUMS OF 440 FT MSL; AS WE DSNDED THROUGH 300 FT MSL; THE VNAV FUNCTION MALFUNCTIONED. THE FLT DIRECTOR SLOWLY COMMANDED A LEVELOFF AND THE VDI SLOWLY SHOWED THE NEED TO LEVEL OFF. THE APCH ON THE FMS SHOWED A 3.14 DEG GS ALL THE WAY TO THE RWY. MY FO STATED THAT THIS PHENOMENON IS OBSERVED ALL THE TIME ON RWY 22L AT JFK. SINCE WE CAN NOW GO BELOW MDA WITHOUT SEEING THE PAPI THIS IS A REAL PROB HERE AT JFK. SINCE THE PROB IS COMPUTER GENERATED BY THE AIRPLANE IT IS NOT SOMETHING THAT THE ARPT AT JFK HAS DONE. IT'S VERY DISCONCERTING TO BE SHOWN INACCURATE GS INFO BELOW MDA. IN WORST CASE A CREW WOULD LOSE GS INFO BELOW 300 FT AND NOT BE ABLE TO SEE THE PAPI EITHER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER AMENDED HIS NARRATIVE TO INDICATE THAT DESCENT BELOW THE MDA IS AUTHORIZED WITH APCH LIGHT COMPONENTS IN VIEW. THE COMMENT REGARDING THE PAPI WAS MISLEADING IN THIS REGARD. REPORTER'S CONCERN IS THAT; UNLIKE THE ACR'S TRAINING EXERCISE -- WHICH WAS A STRAIGHT-IN APCH WITH CONTINUED GS GUIDANCE UNTIL TOUCHDOWN -- THIS APCH ELIMINATES THE GS GUIDANCE AT THE MAP AND CONTINUED DESCENT BELOW MDA MUST BE ACCOMPLISHED WITH NO GLIDE PATH MONITOR AVAILABLE. THE SITUATION HAS BEEN DISCUSSED WITH THE ACR FLT TRAINING DEPARTMENT WITHOUT A SATISFACTORY RESOLUTION OF THE REPORTER'S CONCERNS. REPORTER HAS SUGGESTED THAT TRAINING SHOULD INCLUDE BOTH THE STRAIGHT-IN SCENARIO AND THE ONE THAT EXISTS AT JFK. HE FEELS DESCENT BELOW THE MDA AT JFK SHOULD NOT BE AUTHORIZED DUE TO THE LACK OF GLIDE PATH GUIDANCE.

Data retrieved from NASA's ASRS site as of January 2009 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.