Confusion about clrncs for 2 aircraft of the same air carrier, and with similar call signs.

Attributes
ACN	129752
Time
Date	198911
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : aml airport : iad
State Reference	VA
Altitude	msl bound lower : 9000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : iad
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport
Flight Phase	climbout : intermediate altitude
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 15000 flight time type : 5000
ASRS Report	129752
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 9000 flight time type : 2000
ASRS Report	129509
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

On departure from iad, we were given several headings and altitude changes. Last assigned altitude was 10000' on 050 degree heading. Our flight was air carrier Z xyz. Air carrier X xyp departed behind us. Each heading and altitude change was answered with 'air carrier a xyz,' very clearly by copilot. Out of 9700', ATC asked our altitude and told ut so descend back to 9000'. Flight xyp was then given an altitude change. Neither flight xyp or ATC ever questioned our readback of altitude assignments.

Original NASA ASRS Text

Title: CONFUSION ABOUT CLRNCS FOR 2 ACFT OF THE SAME ACR, AND WITH SIMILAR CALL SIGNS.

Narrative: ON DEP FROM IAD, WE WERE GIVEN SEVERAL HDGS AND ALT CHANGES. LAST ASSIGNED ALT WAS 10000' ON 050 DEG HDG. OUR FLT WAS ACR Z XYZ. ACR X XYP DEPARTED BEHIND US. EACH HDG AND ALT CHANGE WAS ANSWERED WITH 'ACR A XYZ,' VERY CLEARLY BY COPLT. OUT OF 9700', ATC ASKED OUR ALT AND TOLD UT SO DSND BACK TO 9000'. FLT XYP WAS THEN GIVEN AN ALT CHANGE. NEITHER FLT XYP OR ATC EVER QUESTIONED OUR READBACK OF ALT ASSIGNMENTS.

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.