<< >> NASA ASRS Report 544493, April 2002

Altitude overshot on lynsy RNAV arrival procedure by B757 flight crew when the FMS failed to follow the programmed descent profile into las, nv.

Attributes
ACN	544493
Time
Date	200204
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	intersection : lynsy
State Reference	NV
Altitude	msl bound lower : 11600 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : l30.tracon
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : lynsy
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : atp pilot : flight engineer
Experience	flight time total : 10000 flight time type : 3150
ASRS Report	544493
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude flight crew : overrode automation other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

On the lynsy RNAV arrival into las, while executing a VNAV stepdown procedure, the autoplt failed to capture a required crossing altitude. I disconnected the autoplt at the same time the first officer did, and we returned to 12000 ft MSL from approximately 11600 ft, which was the lowest altitude for this deviation. I checked the FMS and MCP which were all correctly set. The crossing altitudes and airspds were part of the arrival database and had not been altered for this fix. Following this excursion, we closely monitored the arrival while the first officer hand flew the aircraft. I noted no further deviations of the flight director pitch instructions. I have no idea why this deviation occurred except possibly a VNAV error. Our airline procedures dictate putting the lowest arrival altitude in the MCP altitude window, which we did.

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Original NASA ASRS Text

Title: ALT OVERSHOT ON LYNSY RNAV ARR PROC BY B757 FLC WHEN THE FMS FAILED TO FOLLOW THE PROGRAMMED DSCNT PROFILE INTO LAS, NV.

Narrative: ON THE LYNSY RNAV ARR INTO LAS, WHILE EXECUTING A VNAV STEPDOWN PROC, THE AUTOPLT FAILED TO CAPTURE A REQUIRED XING ALT. I DISCONNECTED THE AUTOPLT AT THE SAME TIME THE FO DID, AND WE RETURNED TO 12000 FT MSL FROM APPROX 11600 FT, WHICH WAS THE LOWEST ALT FOR THIS DEV. I CHKED THE FMS AND MCP WHICH WERE ALL CORRECTLY SET. THE XING ALTS AND AIRSPDS WERE PART OF THE ARR DATABASE AND HAD NOT BEEN ALTERED FOR THIS FIX. FOLLOWING THIS EXCURSION, WE CLOSELY MONITORED THE ARR WHILE THE FO HAND FLEW THE ACFT. I NOTED NO FURTHER DEVS OF THE FLT DIRECTOR PITCH INSTRUCTIONS. I HAVE NO IDEA WHY THIS DEV OCCURRED EXCEPT POSSIBLY A VNAV ERROR. OUR AIRLINE PROCS DICTATE PUTTING THE LOWEST ARR ALT IN THE MCP ALT WINDOW, WHICH WE DID.

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.