Approach controller issued descent clearance which was slightly garbled. Pilot reads back clearance ...

Attributes
ACN	160883
Time
Date	199010
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lax
State Reference	CA
Altitude	msl bound lower : 20000 msl bound upper : 25000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : edw tracon : iah
Operator	other
Make Model Name	Fighter
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Fighter
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : military
Function	flight crew : captain oversight : pic
Qualification	pilot : military
Experience	flight time last 90 days : 150 flight time total : 5000
ASRS Report	160883
Person 2
Affiliation	government : military
Function	flight crew : captain oversight : pic
Qualification	pilot : military
Experience	flight time last 90 days : 150 flight time total : 2300
ASRS Report	160841
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 1000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Flight of 2 fgt's X on an E-12A/B stereotype route from NAS miramar to R2508 china lake in support of a cno project. At FL250 approximately 25 NM southwest of palmdale, flight (fgt X lead, fgt xx wingman) was passed over from ZLA to edw approach on frequency 269.1. Following chkin at FL250, approach gave a clearance to fgt X to descend to FL180, expedite through FL230 and pilot's discretion to FL180. Fgt X read back clearance and started descend. Passing approximately FL210 approach queried fgt'x altitude with a reply from fgt X, and then immediately climb to FL220 stating that clearance for descent was for another flight (fgt Y). Fgt X and flight initiated an immediate climb bottoming out at approximately 20500' MSL. As flight is about to level at FL220, the conflicting traffic was observed at approximately 2-3 mi at left 11 O'clock, 1000' above fgt X flight in VFR conditions, heading south. Closest point of approach appeared to be approximately 1 NM latitude, 1000' vertical. Fgt Y never left his altitude block. Several factors led to this event, including: 1) garbled transmission from approach clipping first part of transmission, 2) similar sounding call signs operating on same frequency, and 3) misunderstood clrncs which were acknowledged by wrong aircraft and not caught. Possibility that some of both xmissions were stepped on. Recommend military aircraft refrain from using event #south vs aircraft side #south and like sounding call signs. Potential near miss was avoided by staying VFR under positive control.

Original NASA ASRS Text

Title: APCH CTLR ISSUED DESCENT CLRNC WHICH WAS SLIGHTLY GARBLED. PLT READS BACK CLRNC AND STARTS DESCENT. ACFT CONFLICTS WITH ANOTHER ACFT.

Narrative: FLT OF 2 FGT'S X ON AN E-12A/B STEREOTYPE RTE FROM NAS MIRAMAR TO R2508 CHINA LAKE IN SUPPORT OF A CNO PROJECT. AT FL250 APPROX 25 NM SW OF PALMDALE, FLT (FGT X LEAD, FGT XX WINGMAN) WAS PASSED OVER FROM ZLA TO EDW APCH ON FREQ 269.1. FOLLOWING CHKIN AT FL250, APCH GAVE A CLRNC TO FGT X TO DSND TO FL180, EXPEDITE THROUGH FL230 AND PLT'S DISCRETION TO FL180. FGT X READ BACK CLRNC AND STARTED DSND. PASSING APPROX FL210 APCH QUERIED FGT'X ALT WITH A REPLY FROM FGT X, AND THEN IMMEDIATELY CLB TO FL220 STATING THAT CLRNC FOR DSNT WAS FOR ANOTHER FLT (FGT Y). FGT X AND FLT INITIATED AN IMMEDIATE CLB BOTTOMING OUT AT APPROX 20500' MSL. AS FLT IS ABOUT TO LEVEL AT FL220, THE CONFLICTING TFC WAS OBSERVED AT APPROX 2-3 MI AT LEFT 11 O'CLOCK, 1000' ABOVE FGT X FLT IN VFR CONDITIONS, HDG S. CLOSEST POINT OF APCH APPEARED TO BE APPROX 1 NM LAT, 1000' VERT. FGT Y NEVER LEFT HIS ALT BLOCK. SEVERAL FACTORS LED TO THIS EVENT, INCLUDING: 1) GARBLED XMISSION FROM APCH CLIPPING FIRST PART OF XMISSION, 2) SIMILAR SOUNDING CALL SIGNS OPERATING ON SAME FREQ, AND 3) MISUNDERSTOOD CLRNCS WHICH WERE ACKNOWLEDGED BY WRONG ACFT AND NOT CAUGHT. POSSIBILITY THAT SOME OF BOTH XMISSIONS WERE STEPPED ON. RECOMMEND MIL ACFT REFRAIN FROM USING EVENT #S VS ACFT SIDE #S AND LIKE SOUNDING CALL SIGNS. POTENTIAL NEAR MISS WAS AVOIDED BY STAYING VFR UNDER POSITIVE CTL.

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.

Approach controller issued descent clearance which was slightly garbled. Pilot reads back clearance and starts descent. Aircraft conflicts with another aircraft.