Altitude deviation altitude excursion created by clearance interpretation confusion due to phraseolo...

Attributes
ACN	303749
Time
Date	199505
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : oxr
State Reference	CA
Altitude	msl bound lower : 7000 msl bound upper : 9000
Environment
Light	Daylight
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute : direct enroute airway : ntd
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 6200 flight time type : 100
ASRS Report	303749
Person 2
Affiliation	government : military
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Departing smx cleared direct rzs direct oxr, maintain 9000 ft. ZLA switched us over to pt. Magu approach about 30 mi from oxr. We were direct oxr at 9000 ft pt. Magu controller was busy working multiple frequencys. We were able to check-in and asked for direct nelly (a fix on the ILS runway 25 oxr). He said he was unable to do that for traffic. Then after talking to other aircraft he said 'maintain 7000 ft, standby' and went quickly talking to another aircraft. Normally I read back clrncs and report leaving altitudes. He was very busy and saying 'standby' meant to me, he didn't want a readback at that time, but I should comply with his instruction to leave 9000 ft for 7000 ft. At 8500 ft he asked why we're not at 9000 ft then said maintain present altitude. We maintained 8500 ft and soon were cleared (again) down to 7000 ft. Also when we initially checked into pt. Magu approach he asked our assigned heading indicating he was unaware of our navigation (we were direct to oxr). There was no traffic conflict but I felt that issuing an altitude followed by the word 'standby' is not a good practice by a controller. Does it mean standby with readback or standby with execution of ATC clearance? Other contributing factor: high work load for controller.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION CREATED BY CLRNC INTERP CONFUSION DUE TO PHRASEOLOGY AND TRACON APCH CTLR TECHNIQUE ATC COM.

Narrative: DEPARTING SMX CLRED DIRECT RZS DIRECT OXR, MAINTAIN 9000 FT. ZLA SWITCHED US OVER TO PT. MAGU APCH ABOUT 30 MI FROM OXR. WE WERE DIRECT OXR AT 9000 FT PT. MAGU CTLR WAS BUSY WORKING MULTIPLE FREQS. WE WERE ABLE TO CHK-IN AND ASKED FOR DIRECT NELLY (A FIX ON THE ILS RWY 25 OXR). HE SAID HE WAS UNABLE TO DO THAT FOR TFC. THEN AFTER TALKING TO OTHER ACFT HE SAID 'MAINTAIN 7000 FT, STANDBY' AND WENT QUICKLY TALKING TO ANOTHER ACFT. NORMALLY I READ BACK CLRNCS AND RPT LEAVING ALTS. HE WAS VERY BUSY AND SAYING 'STANDBY' MEANT TO ME, HE DIDN'T WANT A READBACK AT THAT TIME, BUT I SHOULD COMPLY WITH HIS INSTRUCTION TO LEAVE 9000 FT FOR 7000 FT. AT 8500 FT HE ASKED WHY WE'RE NOT AT 9000 FT THEN SAID MAINTAIN PRESENT ALT. WE MAINTAINED 8500 FT AND SOON WERE CLRED (AGAIN) DOWN TO 7000 FT. ALSO WHEN WE INITIALLY CHKED INTO PT. MAGU APCH HE ASKED OUR ASSIGNED HDG INDICATING HE WAS UNAWARE OF OUR NAV (WE WERE DIRECT TO OXR). THERE WAS NO TFC CONFLICT BUT I FELT THAT ISSUING AN ALT FOLLOWED BY THE WORD 'STANDBY' IS NOT A GOOD PRACTICE BY A CTLR. DOES IT MEAN STANDBY WITH READBACK OR STANDBY WITH EXECUTION OF ATC CLRNC? OTHER CONTRIBUTING FACTOR: HIGH WORK LOAD FOR CTLR.

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.

Altitude deviation altitude excursion created by clearance interpretation confusion due to phraseology and TRACON approach controller technique ATC communication.