Aircraft in slow descent conflicted with another aircraft.

Attributes
ACN	107394
Time
Date	198903
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : aml
State Reference	VA
Altitude	msl bound lower : 10000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : sjo
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	arrival other enroute airway : iad
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 carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 8000 flight time type : 1000
ASRS Report	107394
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 12000 flight time type : 500
ASRS Report	107104
Events
Anomaly	altitude deviation : undershoot conflict : airborne less severe non adherence : required legal separation non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Air carrier X from roc-iad on 3/xx/89 was on a vector south from robrt intersection at 10000' MSL. ATC gave us a clearance to 5000'. I was the PF. The captain was talking on the radio. The captain asked the controller for pd descent. I heard the controller say, 'maintain 7000,' and I stayed to descend. The captain said the controller said, 'maintain 7000' pd.' I twice asked the captain if he was sure the controller said, 'pd.' the captain said he was sure, so I started at 10000'. The controller called traffic ahead of us at 10000' and gave us a heading to 270 degrees and descended us to 7000'. The controller also called out traffic at 2 O'clock 9000' that would conflict with our newly assigned heading and descent. He told us to maintain visibility on that traffic. I started a slow descent because of the conflicting traffic at 9000'. The controller then commanded a right 360 degree turn back to a southerly heading and maintain 4000'. No evasive action was taken. To avoid incidents like this in the future pilots and controllers should never substitute the term 'pd' for 'pilot's discretion.'

Original NASA ASRS Text

Title: ACFT IN SLOW DESCENT CONFLICTED WITH ANOTHER ACFT.

Narrative: ACR X FROM ROC-IAD ON 3/XX/89 WAS ON A VECTOR S FROM ROBRT INTXN AT 10000' MSL. ATC GAVE US A CLRNC TO 5000'. I WAS THE PF. THE CAPT WAS TALKING ON THE RADIO. THE CAPT ASKED THE CTLR FOR PD DSCNT. I HEARD THE CTLR SAY, 'MAINTAIN 7000,' AND I STAYED TO DSND. THE CAPT SAID THE CTLR SAID, 'MAINTAIN 7000' PD.' I TWICE ASKED THE CAPT IF HE WAS SURE THE CTLR SAID, 'PD.' THE CAPT SAID HE WAS SURE, SO I STARTED AT 10000'. THE CTLR CALLED TFC AHEAD OF US AT 10000' AND GAVE US A HDG TO 270 DEGS AND DSNDED US TO 7000'. THE CTLR ALSO CALLED OUT TFC AT 2 O'CLOCK 9000' THAT WOULD CONFLICT WITH OUR NEWLY ASSIGNED HDG AND DSCNT. HE TOLD US TO MAINTAIN VIS ON THAT TFC. I STARTED A SLOW DSCNT BECAUSE OF THE CONFLICTING TFC AT 9000'. THE CTLR THEN COMMANDED A RIGHT 360 DEG TURN BACK TO A SOUTHERLY HDG AND MAINTAIN 4000'. NO EVASIVE ACTION WAS TAKEN. TO AVOID INCIDENTS LIKE THIS IN THE FUTURE PLTS AND CTLRS SHOULD NEVER SUBSTITUTE THE TERM 'PD' FOR 'PLT'S DISCRETION.'

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.