A GLF4 crew on final to iad prematurely departed their assigned altitude without ATC approval.

Attributes
ACN	545147
Time
Date	200204
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : iad.airport
State Reference	DC
Altitude	msl bound lower : 3600 msl bound upper : 4000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : iad.tracon
Operator	general aviation : corporate
Make Model Name	Gulfstream IV
Operating Under FAR Part	Part 91
Navigation In Use	ils localizer & glide slope : 01
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 90 flight time total : 11000 flight time type : 2000
ASRS Report	545147
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	atc equipment other atc equipment : radar other controllera other flight crewa
Resolutory Action	controller : issued alert flight crew : executed go around flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew other
Supplementary
Problem Areas	Airport Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Contacted dulles approach and requested runway 1R for landing and was told that it was not available this night. We were set up to use the right runway as it is the most convenient one for our use. We quickly switched all the data to the left runway and did a fast brief on downwind leg. We were given an altitude of 4000 ft and a vector to intercept the localizer. After intercepting the localizer, we had a TCASII fail message with an accompanying 'bong' every 5-10 seconds that we were not able to cancel. We noticed that the GS was moving and I asked the controller if we were cleared for the approach. The controller asked if we could maintain 4000 ft until the next fix before commencing with the approach. I determined that this would put us 800 ft higher than normal, but acceptable considering WX and runway length. At this time, the non cancelable TCASII fail 'bong' was going on and off every 2-3 seconds. I looked down at the transponder head and selected the stand-by transponder in hopes of canceling this annoying distraction. When I looked up, we were at 3600 ft and I realized that the flying first officer had selected the approach mode on the autoplt, anticipating a clearance for the approach. The autoplt had captured the GS and started down. I reselected flight level change to get back to 4000 ft and at the same time the controller asked if we had started down on our own. I said no, we had a GS capture, and a short time later she cleared us for the approach and we started down with a constant 'bong' going on and off. At 3000 ft and 5 mi, we decided that with all the nonstandard approach and distrs to not continue and requested a go around for another approach. The bong still could not be canceled and was going off and on continuously. The second approach was accomplished at the normal expected altitude and clrncs with the constant alerting message of the TCASII fail and bonging the entire time, and did not stop until we were on the ground and able to turn off the transponder.

Original NASA ASRS Text

Title: A GLF4 CREW ON FINAL TO IAD PREMATURELY DEPARTED THEIR ASSIGNED ALT WITHOUT ATC APPROVAL.

Narrative: CONTACTED DULLES APCH AND REQUESTED RWY 1R FOR LNDG AND WAS TOLD THAT IT WAS NOT AVAILABLE THIS NIGHT. WE WERE SET UP TO USE THE R RWY AS IT IS THE MOST CONVENIENT ONE FOR OUR USE. WE QUICKLY SWITCHED ALL THE DATA TO THE L RWY AND DID A FAST BRIEF ON DOWNWIND LEG. WE WERE GIVEN AN ALT OF 4000 FT AND A VECTOR TO INTERCEPT THE LOC. AFTER INTERCEPTING THE LOC, WE HAD A TCASII FAIL MESSAGE WITH AN ACCOMPANYING 'BONG' EVERY 5-10 SECONDS THAT WE WERE NOT ABLE TO CANCEL. WE NOTICED THAT THE GS WAS MOVING AND I ASKED THE CTLR IF WE WERE CLRED FOR THE APCH. THE CTLR ASKED IF WE COULD MAINTAIN 4000 FT UNTIL THE NEXT FIX BEFORE COMMENCING WITH THE APCH. I DETERMINED THAT THIS WOULD PUT US 800 FT HIGHER THAN NORMAL, BUT ACCEPTABLE CONSIDERING WX AND RWY LENGTH. AT THIS TIME, THE NON CANCELABLE TCASII FAIL 'BONG' WAS GOING ON AND OFF EVERY 2-3 SECONDS. I LOOKED DOWN AT THE XPONDER HEAD AND SELECTED THE STAND-BY XPONDER IN HOPES OF CANCELING THIS ANNOYING DISTR. WHEN I LOOKED UP, WE WERE AT 3600 FT AND I REALIZED THAT THE FLYING FO HAD SELECTED THE APCH MODE ON THE AUTOPLT, ANTICIPATING A CLRNC FOR THE APCH. THE AUTOPLT HAD CAPTURED THE GS AND STARTED DOWN. I RESELECTED FLT LEVEL CHANGE TO GET BACK TO 4000 FT AND AT THE SAME TIME THE CTLR ASKED IF WE HAD STARTED DOWN ON OUR OWN. I SAID NO, WE HAD A GS CAPTURE, AND A SHORT TIME LATER SHE CLRED US FOR THE APCH AND WE STARTED DOWN WITH A CONSTANT 'BONG' GOING ON AND OFF. AT 3000 FT AND 5 MI, WE DECIDED THAT WITH ALL THE NONSTANDARD APCH AND DISTRS TO NOT CONTINUE AND REQUESTED A GAR FOR ANOTHER APCH. THE BONG STILL COULD NOT BE CANCELED AND WAS GOING OFF AND ON CONTINUOUSLY. THE SECOND APCH WAS ACCOMPLISHED AT THE NORMAL EXPECTED ALT AND CLRNCS WITH THE CONSTANT ALERTING MESSAGE OF THE TCASII FAIL AND BONGING THE ENTIRE TIME, AND DID NOT STOP UNTIL WE WERE ON THE GND AND ABLE TO TURN OFF THE XPONDER.

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.