A B777 flight crew turns to avoid a WX cell without a clearance, while on radar vectors with pct TRA...

Attributes
ACN	630628
Time
Date	200409
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : iad.airport
State Reference	VA
Altitude	msl single value : 4000
Environment
Weather Elements	Rain Thunderstorm
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pct.tracon
Operator	common carrier : air carrier
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	arrival : on vectors arrival star : jasen
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : pct.tracon
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : intermediate altitude
Route In Use	arrival : on vectors arrival star : jasen
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 150 flight time total : 13000 flight time type : 1200
ASRS Report	630628
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 180 flight time total : 13000 flight time type : 400
ASRS Report	630456
Events
Anomaly	inflight encounter : weather non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : wx radar other flight crewa
Resolutory Action	flight crew : took precautionary avoidance action
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Weather ATC Human Performance Environmental Factor Flight Crew Human Performance
Primary Problem	Weather

Narrative:

We were in a line of airplanes being vectored off of the jasen arrival to runways 1L and 1R at iad. Our radar indicated a red cell with steep gradient at 25 NM right in the middle of the final approach course. The aircraft in front of us were all being vectored off a left base on a dogleg to final which turned them inside of the cell. We were 90 degrees off of final heading (heading 090 degrees) at 2 NM from the final approach course and the cell and were switched to the final controller's frequency. I advocated to the captain that we should get a turn as the other airplanes in front of us had to avoid the cell. He tried to call them twice with no reply, so we decided to turn without their approval to avoid the cell. We were looking at TCAS and still had good separation from the airplane in front of us (5 NM) even after the turn. The controller then called us and asked us what heading we were flying. The captain told him we had turned to avoid a 'storm.' he responded with 'you must get approval to turn, you just can't turn on your own, there's no storm out there.' our fom under en route storm area avoidance, states that most ATC radars are l-band and can't detect storms but only precipitation. That was all that was said and we never lost separation and landed uneventfully.

Original NASA ASRS Text

Title: A B777 FLT CREW TURNS TO AVOID A WX CELL WITHOUT A CLRNC, WHILE ON RADAR VECTORS WITH PCT TRACON.

Narrative: WE WERE IN A LINE OF AIRPLANES BEING VECTORED OFF OF THE JASEN ARR TO RWYS 1L AND 1R AT IAD. OUR RADAR INDICATED A RED CELL WITH STEEP GRADIENT AT 25 NM RIGHT IN THE MIDDLE OF THE FINAL APCH COURSE. THE ACFT IN FRONT OF US WERE ALL BEING VECTORED OFF A L BASE ON A DOGLEG TO FINAL WHICH TURNED THEM INSIDE OF THE CELL. WE WERE 90 DEGS OFF OF FINAL HDG (HDG 090 DEGS) AT 2 NM FROM THE FINAL APCH COURSE AND THE CELL AND WERE SWITCHED TO THE FINAL CTLR'S FREQ. I ADVOCATED TO THE CAPT THAT WE SHOULD GET A TURN AS THE OTHER AIRPLANES IN FRONT OF US HAD TO AVOID THE CELL. HE TRIED TO CALL THEM TWICE WITH NO REPLY, SO WE DECIDED TO TURN WITHOUT THEIR APPROVAL TO AVOID THE CELL. WE WERE LOOKING AT TCAS AND STILL HAD GOOD SEPARATION FROM THE AIRPLANE IN FRONT OF US (5 NM) EVEN AFTER THE TURN. THE CTLR THEN CALLED US AND ASKED US WHAT HDG WE WERE FLYING. THE CAPT TOLD HIM WE HAD TURNED TO AVOID A 'STORM.' HE RESPONDED WITH 'YOU MUST GET APPROVAL TO TURN, YOU JUST CAN'T TURN ON YOUR OWN, THERE'S NO STORM OUT THERE.' OUR FOM UNDER ENRTE STORM AREA AVOIDANCE, STATES THAT MOST ATC RADARS ARE L-BAND AND CAN'T DETECT STORMS BUT ONLY PRECIPITATION. THAT WAS ALL THAT WAS SAID AND WE NEVER LOST SEPARATION AND LANDED UNEVENTFULLY.

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 B777 flight crew turns to avoid a WX cell without a clearance, while on radar vectors with pct TRACON.