Commuter flight crew misinterprets clearance via a transition as clearance for a descent.

Attributes
ACN	129591
Time
Date	198911
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mlp airport : mso
State Reference	ID
Altitude	msl bound lower : 9600 msl bound upper : 13000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other descent other
Route In Use	enroute airway : mso enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 215 flight time total : 3400 flight time type : 1000
ASRS Report	129591
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While en route from spokane, wa to missoula, mt, approximately 35 mi east of the mullin pass VOR descending from 17,000 to 13,000' MSL, salt lake center cleared our aircraft to the kona NDB/LOM via the mullin pass transition. It was at this point where the incident occurred. We were handed off to missoula approach and reported ddg to 9600 MSL (the transition (initial) altitude). Approach immediately gave an air carrier flight (who was on the ILS 3 runway 11 approach) a clearance (forgotten) because another airplane had busted a clearance (us), followed by our clearance to maintain 13,000, and hold at kona to be #2 for the approach. The point of contention is: did salt lake center tell us to maintain 13,000 at the end of the clearance to kona? If so, we did miss the altitude assignment. If salt lake did not give the altitude restriction, were we mistaken in continuing down to the initial transition after the clearance, when our previously assigned altitude was 13,000? A contributing factor may have been center saying 'expect no delay for the approach', while en route.

Original NASA ASRS Text

Title: COMMUTER FLT CREW MISINTERPRETS CLRNC VIA A TRANSITION AS CLRNC FOR A DESCENT.

Narrative: WHILE ENRTE FROM SPOKANE, WA TO MISSOULA, MT, APPROX 35 MI E OF THE MULLIN PASS VOR DESCENDING FROM 17,000 TO 13,000' MSL, SALT LAKE CENTER CLRED OUR ACFT TO THE KONA NDB/LOM VIA THE MULLIN PASS TRANSITION. IT WAS AT THIS POINT WHERE THE INCIDENT OCCURRED. WE WERE HANDED OFF TO MISSOULA APCH AND REPORTED DDG TO 9600 MSL (THE TRANSITION (INITIAL) ALT). APCH IMMEDIATELY GAVE AN ACR FLT (WHO WAS ON THE ILS 3 RWY 11 APCH) A CLRNC (FORGOTTEN) BECAUSE ANOTHER AIRPLANE HAD BUSTED A CLRNC (US), FOLLOWED BY OUR CLRNC TO MAINTAIN 13,000, AND HOLD AT KONA TO BE #2 FOR THE APCH. THE POINT OF CONTENTION IS: DID SALT LAKE CENTER TELL US TO MAINTAIN 13,000 AT THE END OF THE CLRNC TO KONA? IF SO, WE DID MISS THE ALT ASSIGNMENT. IF SALT LAKE DID NOT GIVE THE ALT RESTRICTION, WERE WE MISTAKEN IN CONTINUING DOWN TO THE INITIAL TRANSITION AFTER THE CLRNC, WHEN OUR PREVIOUSLY ASSIGNED ALT WAS 13,000? A CONTRIBUTING FACTOR MAY HAVE BEEN CENTER SAYING 'EXPECT NO DELAY FOR THE APCH', WHILE ENRTE.

Data retrieved from NASA's ASRS site as of August 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.