Altitude deviation altitude excursion.

Attributes
ACN	218897
Time
Date	199208
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : stw
State Reference	NJ
Altitude	msl bound lower : 23000 msl bound upper : 23400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny tower : bur
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 225 flight time total : 9000 flight time type : 750
ASRS Report	218897
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation other

Narrative:

At ATC request, doing mach .82 or better descent for spacing into jfk. FMC programmed for .82 descent, be level 10 NM west stw FL230, then cross lindy FL190 at 250 KTS. Full VNAV descent. Aircraft made 10 NM west stw at FL230, but went into altitude hold and speed mode. Inserted FL230 into FMC (cruise page) and 300 KTS descent speed as aircraft was at about 325 KTS. The FMC mach/airspeed changeover did not occur. When FL230 inserted into cruise page and VNAV selected, aircraft started to climb. At FL233, I disconnected autoplt and eased nose back down for descent to FL230. We were above FL233 about 15 seconds, reaching about 23450 ft. ATC did not question or comment on the altitude deviation. Once back at FL230, the computer was checked that all entries were correct. No corrections were needed. Autoplt, LNAV, and VNAV re-engaged. Lindy speed/altitude crossing made with no manual intervention.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION.

Narrative: AT ATC REQUEST, DOING MACH .82 OR BETTER DSCNT FOR SPACING INTO JFK. FMC PROGRAMMED FOR .82 DSCNT, BE LEVEL 10 NM W STW FL230, THEN CROSS LINDY FL190 AT 250 KTS. FULL VNAV DSCNT. ACFT MADE 10 NM W STW AT FL230, BUT WENT INTO ALT HOLD AND SPD MODE. INSERTED FL230 INTO FMC (CRUISE PAGE) AND 300 KTS DSCNT SPD AS ACFT WAS AT ABOUT 325 KTS. THE FMC MACH/AIRSPD CHANGEOVER DID NOT OCCUR. WHEN FL230 INSERTED INTO CRUISE PAGE AND VNAV SELECTED, ACFT STARTED TO CLB. AT FL233, I DISCONNECTED AUTOPLT AND EASED NOSE BACK DOWN FOR DSCNT TO FL230. WE WERE ABOVE FL233 ABOUT 15 SECONDS, REACHING ABOUT 23450 FT. ATC DID NOT QUESTION OR COMMENT ON THE ALTDEV. ONCE BACK AT FL230, THE COMPUTER WAS CHKED THAT ALL ENTRIES WERE CORRECT. NO CORRECTIONS WERE NEEDED. AUTOPLT, LNAV, AND VNAV RE-ENGAGED. LINDY SPD/ALT XING MADE WITH NO MANUAL INTERVENTION.

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.