A B737 flight crew descends to 7000 ft. ATC asks if they are going to 6000 ft. With nothing further ...

Attributes
ACN	415930
Time
Date	199809
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ott
State Reference	MO
Altitude	msl bound lower : 6600 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dca
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 5000
ASRS Report	415930
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 7500 flight time type : 5000
ASRS Report	415675
Events
Anomaly	altitude deviation : undershoot conflict : airborne less severe non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Miss Distance	vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were on approach to bwi in daylight, VFR, talking to approach control. We were issued a clearance to 7000 ft and were level at 7000 ft for several mins. The controller asked us to 'confirm we were going down to 6000 ft.' we said 'no,' and also told him 'we were issued 7000 ft.' he proceeded to talk to other aircraft on the frequency and left us very confused. Thinking we were supposed to be at 6000 ft, the captain started descending. I got on the radio and asked to confirm our assigned altitude. He said '7000 ft.' the captain had already descended to 6600 ft and made an immediate correction to 7000 ft. Nothing else was mentioned about it and no evasive action was required. The controller left us very confused and uncomfortable and we weren't completely sure what he wanted from us. Supplemental information from acn 415675: we had passed nottingham and were proceeding towards deale. Normal clearance is to have been cleared to 6000 ft at deale so this felt a little abnormal. The radio was very busy. Several other radio xmissions occurred before we could finally query. At this point we had descended to 6650-6700 ft and immediately returned to 7000 ft. At no time was safety compromised but there was a potential traffic conflict at 6000 ft had we continued. 2 factors led to this potential conflict: 1) the assuming nature of dca concerning our altitude and when it disagreed with our response no follow-up clarification of what was the correct clearance. 2) our assumption dca was correct and we needed to change altitudes. Lessons learned: for me, never assume. When a conflict exists I should maintain what I believe is my last clearance until clarification/confirmation can be obtained. For ATC, don't leave a question/confusion on a clearance open. Once we had given a response that conflicted with his assumption he should have immediately clarified our correct clearance before going on to other traffic.

Original NASA ASRS Text

Title: A B737 FLC DSNDS TO 7000 FT. ATC ASKS IF THEY ARE GOING TO 6000 FT. WITH NOTHING FURTHER SAID, THE PIC DSNDS TOWARDS 6000 FT AND IS TOLD TO MAINTAIN 7000 FT.

Narrative: WE WERE ON APCH TO BWI IN DAYLIGHT, VFR, TALKING TO APCH CTL. WE WERE ISSUED A CLRNC TO 7000 FT AND WERE LEVEL AT 7000 FT FOR SEVERAL MINS. THE CTLR ASKED US TO 'CONFIRM WE WERE GOING DOWN TO 6000 FT.' WE SAID 'NO,' AND ALSO TOLD HIM 'WE WERE ISSUED 7000 FT.' HE PROCEEDED TO TALK TO OTHER ACFT ON THE FREQ AND LEFT US VERY CONFUSED. THINKING WE WERE SUPPOSED TO BE AT 6000 FT, THE CAPT STARTED DSNDING. I GOT ON THE RADIO AND ASKED TO CONFIRM OUR ASSIGNED ALT. HE SAID '7000 FT.' THE CAPT HAD ALREADY DSNDED TO 6600 FT AND MADE AN IMMEDIATE CORRECTION TO 7000 FT. NOTHING ELSE WAS MENTIONED ABOUT IT AND NO EVASIVE ACTION WAS REQUIRED. THE CTLR LEFT US VERY CONFUSED AND UNCOMFORTABLE AND WE WEREN'T COMPLETELY SURE WHAT HE WANTED FROM US. SUPPLEMENTAL INFO FROM ACN 415675: WE HAD PASSED NOTTINGHAM AND WERE PROCEEDING TOWARDS DEALE. NORMAL CLRNC IS TO HAVE BEEN CLRED TO 6000 FT AT DEALE SO THIS FELT A LITTLE ABNORMAL. THE RADIO WAS VERY BUSY. SEVERAL OTHER RADIO XMISSIONS OCCURRED BEFORE WE COULD FINALLY QUERY. AT THIS POINT WE HAD DSNDED TO 6650-6700 FT AND IMMEDIATELY RETURNED TO 7000 FT. AT NO TIME WAS SAFETY COMPROMISED BUT THERE WAS A POTENTIAL TFC CONFLICT AT 6000 FT HAD WE CONTINUED. 2 FACTORS LED TO THIS POTENTIAL CONFLICT: 1) THE ASSUMING NATURE OF DCA CONCERNING OUR ALT AND WHEN IT DISAGREED WITH OUR RESPONSE NO FOLLOW-UP CLARIFICATION OF WHAT WAS THE CORRECT CLRNC. 2) OUR ASSUMPTION DCA WAS CORRECT AND WE NEEDED TO CHANGE ALTS. LESSONS LEARNED: FOR ME, NEVER ASSUME. WHEN A CONFLICT EXISTS I SHOULD MAINTAIN WHAT I BELIEVE IS MY LAST CLRNC UNTIL CLARIFICATION/CONFIRMATION CAN BE OBTAINED. FOR ATC, DON'T LEAVE A QUESTION/CONFUSION ON A CLRNC OPEN. ONCE WE HAD GIVEN A RESPONSE THAT CONFLICTED WITH HIS ASSUMPTION HE SHOULD HAVE IMMEDIATELY CLARIFIED OUR CORRECT CLRNC BEFORE GOING ON TO OTHER TFC.

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.

A B737 flight crew descends to 7000 ft. ATC asks if they are going to 6000 ft. With nothing further said, the PIC descends towards 6000 ft and is told to maintain 7000 ft.