Narrative:

ATIS for lga stated 'ILS to runway 13.' approach cleared us for an 'ILS DME to runway 13, GS out.' the problem with this approach plate is that there is no such thing as a 'DME' ILS for runway 13. There is, however, an ILS localizer approach procedure with a 500 ft MDA if the 2.8 igda fix is available and a 800 ft MDA with no DME. The plate shows 1800 ft from steed in bold print and in non bold print an 800 ft profile to 2.8 DME. When a clearance is received for a DME ILS, GS out, this creates a bit of confusion. Many aircraft on frequency were questioning the clearance, and it definitely created confusion for us too. We interpreted this as 1800 ft to 5.7 DME then a descent no lower than 500 ft until after 2.8 DME. I began the standard 1000-1200 FPM descent at 5.7 mi and was somewhere between 500-800 ft at approximately 2.8 igda ILS. We realized, after the fact, that 800 ft is the intended minimum altitude until after 2.8 mi. We didn't ring any low altitude alarms at approach, tower or GPWS, so the descent was no doubt safe. But, this is an uncomfortable situation with an ambiguous clearance, and an approach plate that needs refinement if approach is going to clear aircraft for an ILS DME. Next time, I definitely would ask for clarification, because both my first officer and myself interpreted the clearance and plate in the same manner even after a very thorough approach briefing. It was only some time after the approach when we were discussing the clearance and the controller's intentions, and the plate's ambiguity that we realized that 800 ft was actually the minimum altitude at 2.8 mi -- not 800 ft to 500 ft. 500 ft is really intended to be descended to after 2.8 mi. A further clarification with the controller would, no doubt, have raised a 'red flag' to bring the actual intent of the plate to the surface. Later investigation of similar plates revealed very few that were similar, and in all cases, the higher of the 2 MDA's was preceded by a significantly higher leveloff altitude prior to descent to either of the 2 MDA's. This is good because it calls one's attention to leveling off at an altitude above both MDA's before final descent is started. At lga, 800 ft is the intermediate and the final altitude for one MDA, while there is still a lower 500 ft MDA. This is definitely not a DME ILS GS out approach and is not particularly 'user friendly' either. Callback conversation with reporter revealed the following information: the captain stated that he had not reported this incident to his company or the FAA. He is looking forward towards retirement which is a very short time away. He agreed with the analyst that there should be 2 approach plates created, 1 for each approach, full ILS and the localizer approach.

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Original NASA ASRS Text

Title: A B737-400 PIC RPT ON THE CONFUSION CREATED BY IMPROPER CHART AND APCH CTLR PHRASEOLOGY FOR AN IAP LOC DME APCH AT LGA, NY.

Narrative: ATIS FOR LGA STATED 'ILS TO RWY 13.' APCH CLRED US FOR AN 'ILS DME TO RWY 13, GS OUT.' THE PROB WITH THIS APCH PLATE IS THAT THERE IS NO SUCH THING AS A 'DME' ILS FOR RWY 13. THERE IS, HOWEVER, AN ILS LOC APCH PROC WITH A 500 FT MDA IF THE 2.8 IGDA FIX IS AVAILABLE AND A 800 FT MDA WITH NO DME. THE PLATE SHOWS 1800 FT FROM STEED IN BOLD PRINT AND IN NON BOLD PRINT AN 800 FT PROFILE TO 2.8 DME. WHEN A CLRNC IS RECEIVED FOR A DME ILS, GS OUT, THIS CREATES A BIT OF CONFUSION. MANY ACFT ON FREQ WERE QUESTIONING THE CLRNC, AND IT DEFINITELY CREATED CONFUSION FOR US TOO. WE INTERPED THIS AS 1800 FT TO 5.7 DME THEN A DSCNT NO LOWER THAN 500 FT UNTIL AFTER 2.8 DME. I BEGAN THE STANDARD 1000-1200 FPM DSCNT AT 5.7 MI AND WAS SOMEWHERE BTWN 500-800 FT AT APPROX 2.8 IGDA ILS. WE REALIZED, AFTER THE FACT, THAT 800 FT IS THE INTENDED MINIMUM ALT UNTIL AFTER 2.8 MI. WE DIDN'T RING ANY LOW ALT ALARMS AT APCH, TWR OR GPWS, SO THE DSCNT WAS NO DOUBT SAFE. BUT, THIS IS AN UNCOMFORTABLE SIT WITH AN AMBIGUOUS CLRNC, AND AN APCH PLATE THAT NEEDS REFINEMENT IF APCH IS GOING TO CLR ACFT FOR AN ILS DME. NEXT TIME, I DEFINITELY WOULD ASK FOR CLARIFICATION, BECAUSE BOTH MY FO AND MYSELF INTERPED THE CLRNC AND PLATE IN THE SAME MANNER EVEN AFTER A VERY THOROUGH APCH BRIEFING. IT WAS ONLY SOME TIME AFTER THE APCH WHEN WE WERE DISCUSSING THE CLRNC AND THE CTLR'S INTENTIONS, AND THE PLATE'S AMBIGUITY THAT WE REALIZED THAT 800 FT WAS ACTUALLY THE MINIMUM ALT AT 2.8 MI -- NOT 800 FT TO 500 FT. 500 FT IS REALLY INTENDED TO BE DSNDED TO AFTER 2.8 MI. A FURTHER CLARIFICATION WITH THE CTLR WOULD, NO DOUBT, HAVE RAISED A 'RED FLAG' TO BRING THE ACTUAL INTENT OF THE PLATE TO THE SURFACE. LATER INVESTIGATION OF SIMILAR PLATES REVEALED VERY FEW THAT WERE SIMILAR, AND IN ALL CASES, THE HIGHER OF THE 2 MDA'S WAS PRECEDED BY A SIGNIFICANTLY HIGHER LEVELOFF ALT PRIOR TO DSCNT TO EITHER OF THE 2 MDA'S. THIS IS GOOD BECAUSE IT CALLS ONE'S ATTN TO LEVELING OFF AT AN ALT ABOVE BOTH MDA'S BEFORE FINAL DSCNT IS STARTED. AT LGA, 800 FT IS THE INTERMEDIATE AND THE FINAL ALT FOR ONE MDA, WHILE THERE IS STILL A LOWER 500 FT MDA. THIS IS DEFINITELY NOT A DME ILS GS OUT APCH AND IS NOT PARTICULARLY 'USER FRIENDLY' EITHER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT STATED THAT HE HAD NOT RPTED THIS INCIDENT TO HIS COMPANY OR THE FAA. HE IS LOOKING FORWARD TOWARDS RETIREMENT WHICH IS A VERY SHORT TIME AWAY. HE AGREED WITH THE ANALYST THAT THERE SHOULD BE 2 APCH PLATES CREATED, 1 FOR EACH APCH, FULL ILS AND THE LOC APCH.

Data retrieved from NASA's ASRS site as of July 2007 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.