<< >> NASA ASRS Report 457010, December 1999

An MD88 flight crew experiences an excursion from their initial approach altitude as the coupled autoplt takes the aircraft down prior to GS intercept 8 mi north of lit, ar.

Attributes
ACN	457010
Time
Date	199912
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lit.airport
State Reference	AR
Altitude	msl bound lower : 2400 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : lit.tracon
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach descent : intermediate altitude
Route In Use	approach : instrument precision arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : lit.tracon
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Navigation In Use	other
Route In Use	approach : visual arrival : on vectors
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : instrument pilot : multi engine pilot : atp pilot : commercial
Experience	flight time last 90 days : 180 flight time total : 7000 flight time type : 5000
ASRS Report	457010
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : published procedure non adherence : clearance other anomaly
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance controller : separated traffic flight crew : regained aircraft control
Miss Distance	horizontal : 3000 vertical : 900
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

During vectors to final (south) at little rock adams field, we were cleared to 3000 ft MSL and given a vector towards final and told to intercept the localizer for runway 18L. The aircraft was on autoplt and intercepted the localizer at 3000 ft MSL. After it intercepted the localizer approximately 15 seconds later, it started down out of 3000 ft (still below the glide path). I clicked off the autoplt and stopped the descent at 2400 ft MSL. The approach controller told us we could level at 2500 ft if we liked. We did. A light aircraft flew across final to runway 18R below us at 1500 ft and approximately 1/2 mi in front. We were never in danger of hitting the other aircraft, however, the approach controller was concerned since we deviated from 3000 ft. Neither the copilot nor I were sure why the aircraft started down. We checked all of our switches and tarp. The localizer was armed and captured. It was a puzzle to us. However, due to good crew coordination and decision to click off the autoplt and hand fly the aircraft, we were able to avert a potentially dangerous conflict.

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Original NASA ASRS Text

Title: AN MD88 FLC EXPERIENCES AN EXCURSION FROM THEIR INITIAL APCH ALT AS THE COUPLED AUTOPLT TAKES THE ACFT DOWN PRIOR TO GS INTERCEPT 8 MI N OF LIT, AR.

Narrative: DURING VECTORS TO FINAL (S) AT LITTLE ROCK ADAMS FIELD, WE WERE CLRED TO 3000 FT MSL AND GIVEN A VECTOR TOWARDS FINAL AND TOLD TO INTERCEPT THE LOC FOR RWY 18L. THE ACFT WAS ON AUTOPLT AND INTERCEPTED THE LOC AT 3000 FT MSL. AFTER IT INTERCEPTED THE LOC APPROX 15 SECONDS LATER, IT STARTED DOWN OUT OF 3000 FT (STILL BELOW THE GLIDE PATH). I CLICKED OFF THE AUTOPLT AND STOPPED THE DSCNT AT 2400 FT MSL. THE APCH CTLR TOLD US WE COULD LEVEL AT 2500 FT IF WE LIKED. WE DID. A LIGHT ACFT FLEW ACROSS FINAL TO RWY 18R BELOW US AT 1500 FT AND APPROX 1/2 MI IN FRONT. WE WERE NEVER IN DANGER OF HITTING THE OTHER ACFT, HOWEVER, THE APCH CTLR WAS CONCERNED SINCE WE DEVIATED FROM 3000 FT. NEITHER THE COPLT NOR I WERE SURE WHY THE ACFT STARTED DOWN. WE CHKED ALL OF OUR SWITCHES AND TARP. THE LOC WAS ARMED AND CAPTURED. IT WAS A PUZZLE TO US. HOWEVER, DUE TO GOOD CREW COORD AND DECISION TO CLICK OFF THE AUTOPLT AND HAND FLY THE ACFT, WE WERE ABLE TO AVERT A POTENTIALLY DANGEROUS CONFLICT.

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.