A commuter aircraft that requests a descent has traffic pointed out. ATC also advises the altitude of the traffic, which is lower than the commuter. The pilot of the commuter misinterprets the pointout as a clearance for a descent.

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Attributes
ACN	119770
Time
Date	198908
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : byi
State Reference	ID
Altitude	msl bound lower : 19000 msl bound upper : 20000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc tower : sfo
Operator	common carrier : air taxi
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 4000 flight time type : 200
ASRS Report	119770
Person 2
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : required legal separation other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	faa : investigated faa : assigned or threatened penalties
Miss Distance	horizontal : 27000 vertical : 400
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cruising at FL200, VMC. Requested lower altitude from ZLC as we approached cloud bases along flight path and altitude. Eager to remain clear of clouds, I was anticipating an immediate clearance to some lower altitude. Center responded with '...traffic at 1 O'clock, 5 mi, opposite direction, FL190' which I interpreted as an advisory, that we were cleared to FL190. I saw the traffic as reported and began descending out of FL200. First officer was still looking for traffic and unaware of descent until altitude alerter sounded. Assuming altitude alerter had not been reset to FL190, I continued descent but asked my first officer 'we were cleared to 19, weren't we?' with his negative reply, I began climbing back to FL200. Subsequently cleared to FL180 and advised by center of possible pilot deviation. Case pending with slc flight standards office.

Original NASA ASRS Text

Title: A COMMUTER ACFT THAT REQUESTS A DESCENT HAS TRAFFIC POINTED OUT. ATC ALSO ADVISES THE ALT OF THE TRAFFIC, WHICH IS LOWER THAN THE COMMUTER. THE PLT OF THE COMMUTER MISINTERPRETS THE POINTOUT AS A CLRNC FOR A DESCENT.

Narrative: CRUISING AT FL200, VMC. REQUESTED LOWER ALT FROM ZLC AS WE APCHED CLOUD BASES ALONG FLT PATH AND ALT. EAGER TO REMAIN CLEAR OF CLOUDS, I WAS ANTICIPATING AN IMMEDIATE CLRNC TO SOME LOWER ALT. CENTER RESPONDED WITH '...TFC AT 1 O'CLOCK, 5 MI, OPPOSITE DIRECTION, FL190' WHICH I INTERPRETED AS AN ADVISORY, THAT WE WERE CLRED TO FL190. I SAW THE TFC AS REPORTED AND BEGAN DESCENDING OUT OF FL200. F/O WAS STILL LOOKING FOR TFC AND UNAWARE OF DSCNT UNTIL ALT ALERTER SOUNDED. ASSUMING ALT ALERTER HAD NOT BEEN RESET TO FL190, I CONTINUED DSCNT BUT ASKED MY F/O 'WE WERE CLRED TO 19, WEREN'T WE?' WITH HIS NEGATIVE REPLY, I BEGAN CLIMBING BACK TO FL200. SUBSEQUENTLY CLRED TO FL180 AND ADVISED BY CENTER OF POSSIBLE PLT DEVIATION. CASE PENDING WITH SLC FLT STANDARDS OFFICE.

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.