Narrative:

I was in between 2 aircraft doing a grand canyon tour. We all entered the dragon corridor at 9500 ft. This tour route specifies that a descent begin abeam the dragons head. Aircraft 1 did not begin descent from 9500 ft to 8500 ft as expected. I slowed to 95 KIAS and began my descent at the appropriate place and time. As we approached the tower of RA chkpoint where we are supposed to be at 8500 ft. It did not appear to me that aircraft 1 was even descending. I crossed tower of RA and wondered if perhaps I had the wrong altimeter setting as aircraft 1 was at least 5-800 ft above me and by now less than 1/4 mi at my 1 O'clock. I was aware that aircraft 2 was in close proximity behind me as I had seen him at my 7 O'clock as we entered the corridor. Not being sure of his position and concentrating on aircraft 1, I was hesitant to maneuver. I attempted to get aircraft 1 to give me permission to pass. I received no reply. By this time we were crossing the river. At this point all aircraft switch from 122.85 to 119.00. What is most likely to have happened is that I was still on 122.85 while aircraft 1 had switched to 119.00. I did not hear him ever call 'the river' which would have been a required call that would have alerted me to which frequency he was on. I assumed aircraft 1 was landing at gcn as this is where they are based. Also by this time he had descended to 8500 ft. I had been at 8500 ft prior to the river and had resumed normal cruising speed. As we exited the corridor, these 2 factors combined to put me past him quickly. At some point aircraft 2 responded to my call to aircraft 1 which further added to the confusion. I passed over top of aircraft 1 by about 100 ft when the gcn tower cleared me to transition the air traffic area. This incident could have been prevented if: I had taken the initiative and queried aircraft 1 as to his intentions when he did not descend at the required point, or if aircraft 1 had flown the route as it is described. Fortunately, once again the concept of see and avoid succeeded where the complexity of the sfar failed.

Google
 

Original NASA ASRS Text

Title: GRAND CANYON TOUR ACFT HAS NMAC WITH ACFT DOING SAME TOUR.

Narrative: I WAS IN BTWN 2 ACFT DOING A GRAND CANYON TOUR. WE ALL ENTERED THE DRAGON CORRIDOR AT 9500 FT. THIS TOUR RTE SPECIFIES THAT A DSCNT BEGIN ABEAM THE DRAGONS HEAD. ACFT 1 DID NOT BEGIN DSCNT FROM 9500 FT TO 8500 FT AS EXPECTED. I SLOWED TO 95 KIAS AND BEGAN MY DSCNT AT THE APPROPRIATE PLACE AND TIME. AS WE APCHED THE TWR OF RA CHKPOINT WHERE WE ARE SUPPOSED TO BE AT 8500 FT. IT DID NOT APPEAR TO ME THAT ACFT 1 WAS EVEN DSNDING. I CROSSED TWR OF RA AND WONDERED IF PERHAPS I HAD THE WRONG ALTIMETER SETTING AS ACFT 1 WAS AT LEAST 5-800 FT ABOVE ME AND BY NOW LESS THAN 1/4 MI AT MY 1 O'CLOCK. I WAS AWARE THAT ACFT 2 WAS IN CLOSE PROX BEHIND ME AS I HAD SEEN HIM AT MY 7 O'CLOCK AS WE ENTERED THE CORRIDOR. NOT BEING SURE OF HIS POS AND CONCENTRATING ON ACFT 1, I WAS HESITANT TO MANEUVER. I ATTEMPTED TO GET ACFT 1 TO GIVE ME PERMISSION TO PASS. I RECEIVED NO REPLY. BY THIS TIME WE WERE XING THE RIVER. AT THIS POINT ALL ACFT SWITCH FROM 122.85 TO 119.00. WHAT IS MOST LIKELY TO HAVE HAPPENED IS THAT I WAS STILL ON 122.85 WHILE ACFT 1 HAD SWITCHED TO 119.00. I DID NOT HEAR HIM EVER CALL 'THE RIVER' WHICH WOULD HAVE BEEN A REQUIRED CALL THAT WOULD HAVE ALERTED ME TO WHICH FREQ HE WAS ON. I ASSUMED ACFT 1 WAS LNDG AT GCN AS THIS IS WHERE THEY ARE BASED. ALSO BY THIS TIME HE HAD DSNDED TO 8500 FT. I HAD BEEN AT 8500 FT PRIOR TO THE RIVER AND HAD RESUMED NORMAL CRUISING SPD. AS WE EXITED THE CORRIDOR, THESE 2 FACTORS COMBINED TO PUT ME PAST HIM QUICKLY. AT SOME POINT ACFT 2 RESPONDED TO MY CALL TO ACFT 1 WHICH FURTHER ADDED TO THE CONFUSION. I PASSED OVER TOP OF ACFT 1 BY ABOUT 100 FT WHEN THE GCN TWR CLRED ME TO TRANSITION THE ATA. THIS INCIDENT COULD HAVE BEEN PREVENTED IF: I HAD TAKEN THE INITIATIVE AND QUERIED ACFT 1 AS TO HIS INTENTIONS WHEN HE DID NOT DSND AT THE REQUIRED POINT, OR IF ACFT 1 HAD FLOWN THE RTE AS IT IS DESCRIBED. FORTUNATELY, ONCE AGAIN THE CONCEPT OF SEE AND AVOID SUCCEEDED WHERE THE COMPLEXITY OF THE SFAR FAILED.

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.