Altitude deviation with respect to airspeed deviation on STAR arrival. A-320 FMC design.

Attributes
ACN	303708
Time
Date	199504
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : gdm
State Reference	MA
Altitude	msl bound lower : 9300 msl bound upper : 10000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bos tower : apf
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : bos
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 20450 flight time type : 1450
ASRS Report	303708
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : published procedure non adherence : clearance other anomaly other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Descending into boston on gardner arrival. Given clearance by ZBW to cross lobby intersection at 8000 ft 230 KTS. Switched to bos approach, passing roughly 13000 ft MSL, with all crossing speed restrs set in FMGC. Constraints showed on navigation display screen. Put in runway 15 ILS approach in mcdu, which promptly dropped the gardner 2 arrival and all constraints. Quickly selected another approach and reentered gardner 2 arrival and original constraints. Asked first officer to check and see what was wrong. When he reselected the ILS runway 15 right approach, the vertical speed which I had set at minus 500 FPM to slow sink rate and speed to 250 KTS for below 10000 ft MSL faulted to an open descent mode dropping out the vertical speed (descent rate) mode and consequently aircraft descended below 10000 ft MSL at 330 KTS. Disconnected autoplt and manually slowed descent rate so aircraft was below 250 KTS by 9300 ft MSL. Computer controled (electronic) aircraft are real nice but can get one in trouble in a hurry when the database is set up differently than center or approach control clrncs. In this case the database is set up to drop the gardner arrival and use the transition to runway 15R ILS which is different. Do not see any solution to this unless the company makes known to ATC what the consequences are if the aircraft database and ATC clrncs don't match up. This could have been a real problem at a lower altitude or in a mountainous area.

Original NASA ASRS Text

Title: ALTDEV WITH RESPECT TO AIRSPD DEV ON STAR ARR. A-320 FMC DESIGN.

Narrative: DSNDING INTO BOSTON ON GARDNER ARR. GIVEN CLRNC BY ZBW TO CROSS LOBBY INTXN AT 8000 FT 230 KTS. SWITCHED TO BOS APCH, PASSING ROUGHLY 13000 FT MSL, WITH ALL XING SPD RESTRS SET IN FMGC. CONSTRAINTS SHOWED ON NAV DISPLAY SCREEN. PUT IN RWY 15 ILS APCH IN MCDU, WHICH PROMPTLY DROPPED THE GARDNER 2 ARR AND ALL CONSTRAINTS. QUICKLY SELECTED ANOTHER APCH AND REENTERED GARDNER 2 ARR AND ORIGINAL CONSTRAINTS. ASKED FO TO CHK AND SEE WHAT WAS WRONG. WHEN HE RESELECTED THE ILS RWY 15 R APCH, THE VERT SPD WHICH I HAD SET AT MINUS 500 FPM TO SLOW SINK RATE AND SPD TO 250 KTS FOR BELOW 10000 FT MSL FAULTED TO AN OPEN DSCNT MODE DROPPING OUT THE VERT SPD (DSCNT RATE) MODE AND CONSEQUENTLY ACFT DSNDED BELOW 10000 FT MSL AT 330 KTS. DISCONNECTED AUTOPLT AND MANUALLY SLOWED DSCNT RATE SO ACFT WAS BELOW 250 KTS BY 9300 FT MSL. COMPUTER CTLED (ELECTRONIC) ACFT ARE REAL NICE BUT CAN GET ONE IN TROUBLE IN A HURRY WHEN THE DATABASE IS SET UP DIFFERENTLY THAN CTR OR APCH CTL CLRNCS. IN THIS CASE THE DATABASE IS SET UP TO DROP THE GARDNER ARR AND USE THE TRANSITION TO RWY 15R ILS WHICH IS DIFFERENT. DO NOT SEE ANY SOLUTION TO THIS UNLESS THE COMPANY MAKES KNOWN TO ATC WHAT THE CONSEQUENCES ARE IF THE ACFT DATABASE AND ATC CLRNCS DON'T MATCH UP. THIS COULD HAVE BEEN A REAL PROB AT A LOWER ALT OR IN A MOUNTAINOUS AREA.

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.