Altitude deviation. Excursion from assigned.

Attributes
ACN	139461
Time
Date	199003
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ffu
State Reference	UT
Altitude	msl bound lower : 31000 msl bound upper : 31700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : atp pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 11000 flight time type : 2500
ASRS Report	139461
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 7500 flight time type : 2500
ASRS Report	139467
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem none taken : unable
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

We were on a scheduled air carrier flight # xx between san and slc. Flight had been cruising at FL370 with ZLC in LNAV and VNAV mode. Slc gave clearance from 370 to 310. First officer was flying and selected 310 in MCP and vertical speed 1000' descent. The 1000' altitude alert sounded at 32000 and callout made. Captain noticed altitude acquire annunciate then altitude hold in green on mode annunciator panel. Aircraft cruised at FL310 for several mins, all normal, in altitude hold at 310. Slc gave xx clearance to cross 5 south of ffu, at 15000', 250 KIAS, altimeter 29.99. 15000' was selected in MCP altitude window. First officer then proceeded to make a waypoint in FMS consisting of the ffu/188/5. While in the process of making the waypoint and discussing with captain, slc requested altitude of xx aircraft was noted climbing through 31500' at approximately 1300 FPM climb. Aircraft was stopped at 31700' and immediately returned to 31000'. MCP window was still at 15000', altitude hold and vertical speed armed. At no time was VNAV used, and at no time was anything on FMS scratch pad placed in the FMS or executed. Waypoint was being built on scratch pad, but not brought up to FMS, used or executed. In addition scratch pad was for descent and VNAV not in use. Autoplt was in 'B' mode use by first officer. LNAV was disconnected and LNAV, VNAV modes not used remainder of flight. On arrival slc, maintenance found 'B' autoplt failed byte test, wrote up and placed on mco and downed 'B' autoplt for maintenance. On subsequent leg (slc-jac) with 'a' autoplt in use, we were unable to engage VNAV mode and discontinued all autoplt LNAV and VNAV operations. Callback conversation with reporter revealed the following: reporter states that both crew members were discussing the CDU inputs and that neither was watching the aircraft so the altitude excursion went unnoticed as there was no aural warning because of the fact that the altitude alerter was set for descent. The autoplt experienced some system failure as it failed the maintenance test upon arrival. There is no normal condition where an input to the CDU will affect the autoplt in the altitude hold mode.

Original NASA ASRS Text

Title: ALT DEVIATION. EXCURSION FROM ASSIGNED.

Narrative: WE WERE ON A SCHEDULED ACR FLT # XX BETWEEN SAN AND SLC. FLT HAD BEEN CRUISING AT FL370 WITH ZLC IN LNAV AND VNAV MODE. SLC GAVE CLRNC FROM 370 TO 310. F/O WAS FLYING AND SELECTED 310 IN MCP AND VERTICAL SPEED 1000' DSCNT. THE 1000' ALT ALERT SOUNDED AT 32000 AND CALLOUT MADE. CAPT NOTICED ALT ACQUIRE ANNUNCIATE THEN ALT HOLD IN GREEN ON MODE ANNUNCIATOR PANEL. ACFT CRUISED AT FL310 FOR SEVERAL MINS, ALL NORMAL, IN ALT HOLD AT 310. SLC GAVE XX CLRNC TO CROSS 5 S OF FFU, AT 15000', 250 KIAS, ALTIMETER 29.99. 15000' WAS SELECTED IN MCP ALT WINDOW. F/O THEN PROCEEDED TO MAKE A WAYPOINT IN FMS CONSISTING OF THE FFU/188/5. WHILE IN THE PROCESS OF MAKING THE WAYPOINT AND DISCUSSING WITH CAPT, SLC REQUESTED ALT OF XX ACFT WAS NOTED CLIMBING THROUGH 31500' AT APPROX 1300 FPM CLIMB. ACFT WAS STOPPED AT 31700' AND IMMEDIATELY RETURNED TO 31000'. MCP WINDOW WAS STILL AT 15000', ALT HOLD AND VERTICAL SPEED ARMED. AT NO TIME WAS VNAV USED, AND AT NO TIME WAS ANYTHING ON FMS SCRATCH PAD PLACED IN THE FMS OR EXECUTED. WAYPOINT WAS BEING BUILT ON SCRATCH PAD, BUT NOT BROUGHT UP TO FMS, USED OR EXECUTED. IN ADDITION SCRATCH PAD WAS FOR DSCNT AND VNAV NOT IN USE. AUTOPLT WAS IN 'B' MODE USE BY F/O. LNAV WAS DISCONNECTED AND LNAV, VNAV MODES NOT USED REMAINDER OF FLT. ON ARR SLC, MAINT FOUND 'B' AUTOPLT FAILED BYTE TEST, WROTE UP AND PLACED ON MCO AND DOWNED 'B' AUTOPLT FOR MAINT. ON SUBSEQUENT LEG (SLC-JAC) WITH 'A' AUTOPLT IN USE, WE WERE UNABLE TO ENGAGE VNAV MODE AND DISCONTINUED ALL AUTOPLT LNAV AND VNAV OPERATIONS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: REPORTER STATES THAT BOTH CREW MEMBERS WERE DISCUSSING THE CDU INPUTS AND THAT NEITHER WAS WATCHING THE ACFT SO THE ALT EXCURSION WENT UNNOTICED AS THERE WAS NO AURAL WARNING BECAUSE OF THE FACT THAT THE ALT ALERTER WAS SET FOR DSCNT. THE AUTOPLT EXPERIENCED SOME SYSTEM FAILURE AS IT FAILED THE MAINT TEST UPON ARR. THERE IS NO NORMAL CONDITION WHERE AN INPUT TO THE CDU WILL AFFECT THE AUTOPLT IN THE ALT HOLD MODE.

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.