Altitude deviation altitude excursion.

Attributes
ACN	203548
Time
Date	199203
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : pit
State Reference	PA
Altitude	msl bound lower : 3700 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : pit tracon : bur
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 190 flight time total : 2000 flight time type : 190
ASRS Report	203548
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Just before intercepting localizer to runway 32 we received a TA on our TCASII immediately followed by an RA to descend. I saw the TCASII displayed an aircraft at 4200 ft (200 ft above our aircraft) and we immediately descended. I contacted approach advising what had happened. Approach cleared us for the ILS 32 and said to climb back up to 4000 ft, and we did accordingly. Approach said they showed no aircraft in the vicinity and we never had visual contact with the 'TCASII aircraft.' approximately once every hour (in my experience) the TCASII displays a 'phony' aircraft for approximately 2 seconds before disappearing. If this 'mirage' appears at the wrong place at the wrong time you get an immediate RA and must immediately act.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION.

Narrative: JUST BEFORE INTERCEPTING LOC TO RWY 32 WE RECEIVED A TA ON OUR TCASII IMMEDIATELY FOLLOWED BY AN RA TO DSND. I SAW THE TCASII DISPLAYED AN ACFT AT 4200 FT (200 FT ABOVE OUR ACFT) AND WE IMMEDIATELY DSNDED. I CONTACTED APCH ADVISING WHAT HAD HAPPENED. APCH CLRED US FOR THE ILS 32 AND SAID TO CLB BACK UP TO 4000 FT, AND WE DID ACCORDINGLY. APCH SAID THEY SHOWED NO ACFT IN THE VICINITY AND WE NEVER HAD VISUAL CONTACT WITH THE 'TCASII ACFT.' APPROX ONCE EVERY HR (IN MY EXPERIENCE) THE TCASII DISPLAYS A 'PHONY' ACFT FOR APPROX 2 SECONDS BEFORE DISAPPEARING. IF THIS 'MIRAGE' APPEARS AT THE WRONG PLACE AT THE WRONG TIME YOU GET AN IMMEDIATE RA AND MUST IMMEDIATELY ACT.

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.