<< >> NASA ASRS Report 276040, June 1994

Reporter issued an incorrect altitude to aircraft 1 which caused the TCASII RA to activate on aircraft 2 at the same altitude. There was no loss of standard separation.

Attributes
ACN	276040
Time
Date	199406
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : btv
State Reference	VT
Altitude	msl bound lower : 4000 msl bound upper : 4000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : btv tower : bdl
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 10
ASRS Report	276040
Person 2
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : investigated Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

While working busy IFR traffic, 2 aircraft were assigned the same altitude, 4000 ft. This induced a TCASII RA in the lead aircraft causing that pilot to descend 300-400 ft below assigned altitude. (Pilot subsequently returned to assigned altitude.) I believed that the trailing aircraft had been issued 5000 ft. At first, I thought the trailing aircraft had violated a 5000 ft altitude assignment. It was not until one week later, while listening to the tape, that I discovered the duplicate altitude assignment. Solutions? Better strip marking, pay closer attention. Question everything.

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Original NASA ASRS Text

Title: RPTR ISSUED AN INCORRECT ALT TO ACFT 1 WHICH CAUSED THE TCASII RA TO ACTIVATE ON ACFT 2 AT THE SAME ALT. THERE WAS NO LOSS OF STANDARD SEPARATION.

Narrative: WHILE WORKING BUSY IFR TFC, 2 ACFT WERE ASSIGNED THE SAME ALT, 4000 FT. THIS INDUCED A TCASII RA IN THE LEAD ACFT CAUSING THAT PLT TO DSND 300-400 FT BELOW ASSIGNED ALT. (PLT SUBSEQUENTLY RETURNED TO ASSIGNED ALT.) I BELIEVED THAT THE TRAILING ACFT HAD BEEN ISSUED 5000 FT. AT FIRST, I THOUGHT THE TRAILING ACFT HAD VIOLATED A 5000 FT ALT ASSIGNMENT. IT WAS NOT UNTIL ONE WK LATER, WHILE LISTENING TO THE TAPE, THAT I DISCOVERED THE DUPLICATE ALT ASSIGNMENT. SOLUTIONS? BETTER STRIP MARKING, PAY CLOSER ATTN. QUESTION EVERYTHING.

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.