Narrative:

Descending via the maier one RNAV arrival we had just passed the 'eddna' fix at 8000 ft and started our descent to 6000 ft for the 'kucoo' fix. Approaching 'cacty' and descending through approximately. 7500 ft the approach controller came on and said something to the effect: 'your altitude is too low for the fix you are over.' he did not state the name of the fix; nor the altitude he thought we should be at. This was very puzzling to us since; according to what we were seeing on our FMS and our mfd; we were well past 'eddna' and approaching 'cacty.' after we double checked the maier one arrival plate and our position at the time (coming up on cacty); I replied: 'approach; on the arrival we show eddna at 8000 ft and kucoo at 6000 ft;' with the emphasis on the word 'at.' the controller shot back in what seemed to be an agitated; raised voice: 'yeah; I show you over eddna and you are supposed to be at 8000 ft.' this did nothing to clear up our confusion because our FMS showed us approaching cacty. Due to the conflicting information between what we were looking at and what the controller was telling us; the PF decided not to descend any further until we got this sorted out; and brought the plane back to 8000 ft. This in turn caused us to be too high for the 6000 ft crossing at kucoo -- the distance between these fixes is very short. In my next radio transmission I stated: 'we showed us crossing eddna at 8000 ft; and descended after eddna.' to which the controller snorted back in a rapid; irritated manner: 'well; if that's true then my scope must be off by miles (we think he said 25 miles ) and I guess I'm going to have to get my supervisor involved.' it did not seem likely that further communication at this point would be beneficial. So we basically ended it; finished flying the arrival and the visual approach to runway 26R. During taxi to the FBO we were given a phone number to call. The shift supervisor that I spoke to was courteous and professional. The supervisor had been briefed but had not had time to look at and listen to the tapes. In our conversation I expressed to our befuddlement that the controller showed us being 'at' eddna and too low when our FMS was showing us well past eddna -- actually closing in on cacty. I stated that both of us felt certain that we had crossed eddna at 8000 ft and 180; and started our descent after crossing eddna. At this point it was indicated that they had been 'having some problems in this area.' as it turns out that eight days prior to our occurrence another professional crew; this time a crew with one of the major airlines; had the exact same experience at the same fix. That crew was also absolutely adamant that they crossed eddna at 8000 ft before descending. Another supervisor at the phoenix TRACON stated to me in a conversation we had two days later that the resemblance between the two incidents was 'uncanny.' he said that the radar plot showed almost identical altitude deviation; starting about the same distance from the same fix. And both crews adamant about having crossed the fix at 8000 ft before descending. According to the TRACON supervisor the radar plot shows our arrival being flown perfectly up to the disputed point; -- crossing the fixes at the prescribed altitudes and speeds; and it shows us level off at 8000 ft for awhile. That fact shows that our full intent was to fly this procedure correctly and as published. I can also say that we were both monitoring the process closely because of the number of altitude and speed changes on this arrival. How we would then have let the airplane descend several hundred ft below the prescribed altitude during a 2 mile span before the fix without either one of us noticing the descent is beyond me. It makes no sense. I am trying to figure out what can be learned from this incident. Knowing that an experienced airline crew had the exact same experience a week before us makes me question whether there might be some kind of intermittent problem or a glitch in either the ground based equipment or possibly in the onboard navigation equipment or database. As I stated before; we both feel strongly that we did not descend until after the fix. So does the other crew. And both crews were monitoring the process closely. One thing I take from this is that controllers need to be very clear and precise in this kind of situation. Clearly state names of fixes or navaids; clearly state desired altitude or speed; and if possible; offer a suggestion to remedy the situation as quickly as possible. After all; we are all in this together; and we all want to do the right thing.callback conversation with reporter revealed the following information: reporter stated that after his discussion with ATC supervisor; he concluded that perhaps the lead turn for the subsequent fix coincided with the point at which they departed the published altitude of 8000 ft. Apparently their FMC initiates the turn prior to the fix equal to a distance of 1% of the ground speed and the next fix becomes the active waypoint.

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Original NASA ASRS Text

Title: C560 FLT CREW WAS INFORMED BY ATC THAT THEY FAILED TO ADHERE TO THE PUBLISHED CROSSING ALT ON THE MAIER ONE STAR.

Narrative: DESCENDING VIA THE MAIER ONE RNAV ARR WE HAD JUST PASSED THE 'EDDNA' FIX AT 8000 FT AND STARTED OUR DSCNT TO 6000 FT FOR THE 'KUCOO' FIX. APCHING 'CACTY' AND DESCENDING THROUGH APPROX. 7500 FT THE APCH CTLR CAME ON AND SAID SOMETHING TO THE EFFECT: 'YOUR ALTITUDE IS TOO LOW FOR THE FIX YOU ARE OVER.' HE DID NOT STATE THE NAME OF THE FIX; NOR THE ALT HE THOUGHT WE SHOULD BE AT. THIS WAS VERY PUZZLING TO US SINCE; ACCORDING TO WHAT WE WERE SEEING ON OUR FMS AND OUR MFD; WE WERE WELL PAST 'EDDNA' AND APCHING 'CACTY.' AFTER WE DOUBLE CHECKED THE MAIER ONE ARR PLATE AND OUR POSITION AT THE TIME (COMING UP ON CACTY); I REPLIED: 'APPROACH; ON THE ARR WE SHOW EDDNA AT 8000 FT AND KUCOO AT 6000 FT;' WITH THE EMPHASIS ON THE WORD 'AT.' THE CTLR SHOT BACK IN WHAT SEEMED TO BE AN AGITATED; RAISED VOICE: 'YEAH; I SHOW YOU OVER EDDNA AND YOU ARE SUPPOSED TO BE AT 8000 FT.' THIS DID NOTHING TO CLEAR UP OUR CONFUSION BECAUSE OUR FMS SHOWED US APCHING CACTY. DUE TO THE CONFLICTING INFORMATION BETWEEN WHAT WE WERE LOOKING AT AND WHAT THE CTLR WAS TELLING US; THE PF DECIDED NOT TO DSND ANY FURTHER UNTIL WE GOT THIS SORTED OUT; AND BROUGHT THE PLANE BACK TO 8000 FT. THIS IN TURN CAUSED US TO BE TOO HIGH FOR THE 6000 FT CROSSING AT KUCOO -- THE DISTANCE BETWEEN THESE FIXES IS VERY SHORT. IN MY NEXT RADIO TRANSMISSION I STATED: 'WE SHOWED US CROSSING EDDNA AT 8000 FT; AND DESCENDED AFTER EDDNA.' TO WHICH THE CTLR SNORTED BACK IN A RAPID; IRRITATED MANNER: 'WELL; IF THAT'S TRUE THEN MY SCOPE MUST BE OFF BY MILES (WE THINK HE SAID 25 MILES ) AND I GUESS I'M GOING TO HAVE TO GET MY SUPERVISOR INVOLVED.' IT DID NOT SEEM LIKELY THAT FURTHER COM AT THIS POINT WOULD BE BENEFICIAL. SO WE BASICALLY ENDED IT; FINISHED FLYING THE ARR AND THE VISUAL APCH TO RWY 26R. DURING TAXI TO THE FBO WE WERE GIVEN A PHONE NUMBER TO CALL. THE SHIFT SUPERVISOR THAT I SPOKE TO WAS COURTEOUS AND PROFESSIONAL. THE SUPERVISOR HAD BEEN BRIEFED BUT HAD NOT HAD TIME TO LOOK AT AND LISTEN TO THE TAPES. IN OUR CONVERSATION I EXPRESSED TO OUR BEFUDDLEMENT THAT THE CTLR SHOWED US BEING 'AT' EDDNA AND TOO LOW WHEN OUR FMS WAS SHOWING US WELL PAST EDDNA -- ACTUALLY CLOSING IN ON CACTY. I STATED THAT BOTH OF US FELT CERTAIN THAT WE HAD CROSSED EDDNA AT 8000 FT AND 180; AND STARTED OUR DSCNT AFTER CROSSING EDDNA. AT THIS POINT IT WAS INDICATED THAT THEY HAD BEEN 'HAVING SOME PROBLEMS IN THIS AREA.' AS IT TURNS OUT THAT EIGHT DAYS PRIOR TO OUR OCCURRENCE ANOTHER PROFESSIONAL CREW; THIS TIME A CREW WITH ONE OF THE MAJOR AIRLINES; HAD THE EXACT SAME EXPERIENCE AT THE SAME FIX. THAT CREW WAS ALSO ABSOLUTELY ADAMANT THAT THEY CROSSED EDDNA AT 8000 FT BEFORE DESCENDING. ANOTHER SUPERVISOR AT THE PHOENIX TRACON STATED TO ME IN A CONVERSATION WE HAD TWO DAYS LATER THAT THE RESEMBLANCE BETWEEN THE TWO INCIDENTS WAS 'UNCANNY.' HE SAID THAT THE RADAR PLOT SHOWED ALMOST IDENTICAL ALTITUDE DEVIATION; STARTING ABOUT THE SAME DISTANCE FROM THE SAME FIX. AND BOTH CREWS ADAMANT ABOUT HAVING CROSSED THE FIX AT 8000 FT BEFORE DSNDING. ACCORDING TO THE TRACON SUPERVISOR THE RADAR PLOT SHOWS OUR ARR BEING FLOWN PERFECTLY UP TO THE DISPUTED POINT; -- CROSSING THE FIXES AT THE PRESCRIBED ALTS AND SPEEDS; AND IT SHOWS US LEVEL OFF AT 8000 FT FOR AWHILE. THAT FACT SHOWS THAT OUR FULL INTENT WAS TO FLY THIS PROC CORRECTLY AND AS PUBLISHED. I CAN ALSO SAY THAT WE WERE BOTH MONITORING THE PROCESS CLOSELY BECAUSE OF THE NUMBER OF ALTITUDE AND SPEED CHANGES ON THIS ARR. HOW WE WOULD THEN HAVE LET THE AIRPLANE DESCEND SEVERAL HUNDRED FT BELOW THE PRESCRIBED ALTITUDE DURING A 2 MILE SPAN BEFORE THE FIX WITHOUT EITHER ONE OF US NOTICING THE DSCNT IS BEYOND ME. IT MAKES NO SENSE. I AM TRYING TO FIGURE OUT WHAT CAN BE LEARNED FROM THIS INCIDENT. KNOWING THAT AN EXPERIENCED AIRLINE CREW HAD THE EXACT SAME EXPERIENCE A WEEK BEFORE US MAKES ME QUESTION WHETHER THERE MIGHT BE SOME KIND OF INTERMITTENT PROBLEM OR A GLITCH IN EITHER THE GROUND BASED EQUIPMENT OR POSSIBLY IN THE ONBOARD NAVIGATION EQUIPMENT OR DATABASE. AS I STATED BEFORE; WE BOTH FEEL STRONGLY THAT WE DID NOT DESCEND UNTIL AFTER THE FIX. SO DOES THE OTHER CREW. AND BOTH CREWS WERE MONITORING THE PROCESS CLOSELY. ONE THING I TAKE FROM THIS IS THAT CTLRS NEED TO BE VERY CLEAR AND PRECISE IN THIS KIND OF SITUATION. CLEARLY STATE NAMES OF FIXES OR NAVAIDS; CLEARLY STATE DESIRED ALTITUDE OR SPEED; AND IF POSSIBLE; OFFER A SUGGESTION TO REMEDY THE SITUATION AS QUICKLY AS POSSIBLE. AFTER ALL; WE ARE ALL IN THIS TOGETHER; AND WE ALL WANT TO DO THE RIGHT THING.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT AFTER HIS DISCUSSION WITH ATC SUPERVISOR; HE CONCLUDED THAT PERHAPS THE LEAD TURN FOR THE SUBSEQUENT FIX COINCIDED WITH THE POINT AT WHICH THEY DEPARTED THE PUBLISHED ALT OF 8000 FT. APPARENTLY THEIR FMC INITIATES THE TURN PRIOR TO THE FIX EQUAL TO A DISTANCE OF 1% OF THE GROUND SPEED AND THE NEXT FIX BECOMES THE ACTIVE WAYPOINT.

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.