Narrative:

I am reporting an unsafe condition in the airbus FMC software. During my descent I was assigned a crossing altitude. I had a wind of 130 KIAS right on my tail, making a mental computation of the profile difficult. I programmed the altitude in the FMC which correctly computed the descent profile and the aircraft was established on the profile. Upon receiving ATIS I noted a runway change. I installed the runway change. At that moment the first flight attendant entered the cockpit with a brief description of a problem occurring in the cabin. Unknown to me, the FMC had removed the crossing restr and recomputed the profile and continued the descent in VNAV without the restr and without warning. Upon discovering this, I informed the controller that it would be impossible to meet the restr. He said, 'no problem, there was no traffic.' I later discovered this is not a malfunction but the normal way the airbus is programmed. Every time the runway is changed even if it does not affect the arrival, all pilot entered restrs are removed and the pilots are not made aware of the changes. This is unsafe. The computer should not remove pilot entered restrs. This takes 'management by exception' to a higher level.

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Original NASA ASRS Text

Title: AN A320 ACFT WITH XING RESTR CLRNC, RPTR CAPT ENTERED RESTR IN FMC AND OBSERVED ACFT ON PROFILE WHILE OBTAINING ATIS. WHEN RPTR ENTERED NEW RWY IN FMC THE RESTR DROPPED OUT AND RPTR WASN'T ABLE TO MAKE IT. HE FAULTS THE ACFT SYS BECAUSE IT DOESN'T PROVIDE A WARNING WHEN RESTRS ARE DROPPED OUT.

Narrative: I AM RPTING AN UNSAFE CONDITION IN THE AIRBUS FMC SOFTWARE. DURING MY DSCNT I WAS ASSIGNED A XING ALT. I HAD A WIND OF 130 KIAS RIGHT ON MY TAIL, MAKING A MENTAL COMPUTATION OF THE PROFILE DIFFICULT. I PROGRAMMED THE ALT IN THE FMC WHICH CORRECTLY COMPUTED THE DSCNT PROFILE AND THE ACFT WAS ESTABLISHED ON THE PROFILE. UPON RECEIVING ATIS I NOTED A RWY CHANGE. I INSTALLED THE RWY CHANGE. AT THAT MOMENT THE FIRST FLT ATTENDANT ENTERED THE COCKPIT WITH A BRIEF DESCRIPTION OF A PROB OCCURRING IN THE CABIN. UNKNOWN TO ME, THE FMC HAD REMOVED THE XING RESTR AND RECOMPUTED THE PROFILE AND CONTINUED THE DSCNT IN VNAV WITHOUT THE RESTR AND WITHOUT WARNING. UPON DISCOVERING THIS, I INFORMED THE CTLR THAT IT WOULD BE IMPOSSIBLE TO MEET THE RESTR. HE SAID, 'NO PROB, THERE WAS NO TFC.' I LATER DISCOVERED THIS IS NOT A MALFUNCTION BUT THE NORMAL WAY THE AIRBUS IS PROGRAMMED. EVERY TIME THE RWY IS CHANGED EVEN IF IT DOES NOT AFFECT THE ARR, ALL PLT ENTERED RESTRS ARE REMOVED AND THE PLTS ARE NOT MADE AWARE OF THE CHANGES. THIS IS UNSAFE. THE COMPUTER SHOULD NOT REMOVE PLT ENTERED RESTRS. THIS TAKES 'MGMNT BY EXCEPTION' TO A HIGHER LEVEL.

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.