Controller catches own error in clearing PA28 to altitude of B747 in iad class B airspace.

Attributes
ACN	458579
Time
Date	199912
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : iad.airport
State Reference	VA
Altitude	msl bound lower : 4000 msl bound upper : 4700
Environment
Flight Conditions	VMC
Weather Elements	Snow
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iad.tracon
Operator	general aviation : personal
Make Model Name	PA-28 Cherokee/Archer II/Dakota/Pillan/Warrior
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude
Route In Use	departure : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : iad.tracon
Operator	common carrier : air carrier
Make Model Name	B747 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent : intermediate altitude descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	other
Function	controller : departure flight crew : single pilot
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 23 flight time total : 7400 flight time type : 675
ASRS Report	458579
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne critical non adherence : published procedure other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance controller : separated traffic flight crew : took evasive action
Miss Distance	horizontal : 10000 vertical : 1000
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance Weather
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

On departure from jyo with radar vector towards bwi approach control airspace. While level at 4000 ft MSL, I was given a climb to 6000 ft on a 060 degree vector. Position was approximately 14 NM north of iad airport. We entered a snowshower in the climb, and at 4700 ft MSL the controller yelled for us to descend immediately to 4000 ft. I did so and acknowledged the request as I descended. Breaking through the snowshower, I saw a B747 at 12 O'clock position about 1000 ft high and 2 mi away. The B747 was turning left under instruction of controller. The controller apologized for frightening us with the 'emergency descent' instructions. He said he had canceled the original climb clearance from 4000 ft to 6000 ft, however, that transmission was not heard. He later said maybe it did not get through and apologized again as he turned us over to bwi approach. He was extremely busy and very harried while we were on his frequency. Other transmission mistakes were made and corrected as we transited the area. WX was VMC with occasional clouds and snow showers at 4000 ft to 7000 ft. The B747 was probably on a vector for the right downwind for runway 1R at dulles. More than 1 transmission was 'stepped on' before we left that frequency.

Original NASA ASRS Text

Title: CTLR CATCHES OWN ERROR IN CLRING PA28 TO ALT OF B747 IN IAD CLASS B AIRSPACE.

Narrative: ON DEP FROM JYO WITH RADAR VECTOR TOWARDS BWI APCH CTL AIRSPACE. WHILE LEVEL AT 4000 FT MSL, I WAS GIVEN A CLB TO 6000 FT ON A 060 DEG VECTOR. POS WAS APPROX 14 NM N OF IAD ARPT. WE ENTERED A SNOWSHOWER IN THE CLB, AND AT 4700 FT MSL THE CTLR YELLED FOR US TO DSND IMMEDIATELY TO 4000 FT. I DID SO AND ACKNOWLEDGED THE REQUEST AS I DSNDED. BREAKING THROUGH THE SNOWSHOWER, I SAW A B747 AT 12 O'CLOCK POS ABOUT 1000 FT HIGH AND 2 MI AWAY. THE B747 WAS TURNING L UNDER INSTRUCTION OF CTLR. THE CTLR APOLOGIZED FOR FRIGHTENING US WITH THE 'EMER DSCNT' INSTRUCTIONS. HE SAID HE HAD CANCELED THE ORIGINAL CLB CLRNC FROM 4000 FT TO 6000 FT, HOWEVER, THAT XMISSION WAS NOT HEARD. HE LATER SAID MAYBE IT DID NOT GET THROUGH AND APOLOGIZED AGAIN AS HE TURNED US OVER TO BWI APCH. HE WAS EXTREMELY BUSY AND VERY HARRIED WHILE WE WERE ON HIS FREQ. OTHER XMISSION MISTAKES WERE MADE AND CORRECTED AS WE TRANSITED THE AREA. WX WAS VMC WITH OCCASIONAL CLOUDS AND SNOW SHOWERS AT 4000 FT TO 7000 FT. THE B747 WAS PROBABLY ON A VECTOR FOR THE R DOWNWIND FOR RWY 1R AT DULLES. MORE THAN 1 XMISSION WAS 'STEPPED ON' BEFORE WE LEFT THAT FREQ.

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.