An air carrier received an lax seavu runway change during descent. The FMS reverted to VNAV speed as...

Attributes
ACN	787579
Time
Date	200805
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : lax.airport
State Reference	CA
Altitude	msl single value : 13500
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : sct.tracon tower : zzz.tower
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	arrival star : seavu
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	787579
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : crossing restriction not met non adherence : clearance non adherence : published procedure
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : detected after the fact
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

We were navigating to lax on the SEAVU1 arrival. Inside of konzl; upon crossing konzl socal approach cleared us to descend via the SEAVU1 for the ILS to runway 24R. I was the non flying pilot and changed the approach in the FMC from the ILS runway 25L to the ILS runway 24R. At the time of the change the aircraft was on autoplt descending VNAV pth; when the airplane reverted to VNAV speed during the runway change. The captain and I were clarifying the runway change with each other and I was verifying the legs for the transition and approach when I then noticed the airplane reverted to VNAV speed and descended below the cataw restriction of 14000 ft or more. Aircraft descended and crossed cataw at 13500 ft. There was no inquiry from ATC nor was there any TA advisories or resolution. VNAV pth was reengaged and the flight continued without further incident. Automation; when it works well is a great thing; but has its pitfalls as well. Those of us who fly in and out of lax frequently know that ATC will change runways on this arrival at an inconvenient and highly distracting time. Both pilots need to monitor any changes to route and verify that the modification has not changed the path as well.

Original NASA ASRS Text

Title: AN ACR RECEIVED AN LAX SEAVU RWY CHANGE DURING DSCNT. THE FMS REVERTED TO VNAV SPD AS THE FMS WAS REPROGRAMMED. THE CATAW ALT CONSTRAINT WAS MISSED BECAUSE THE CREW DID NOT SEE THE MODE REVERSION OUT OF VNAV PATH.

Narrative: WE WERE NAVIGATING TO LAX ON THE SEAVU1 ARR. INSIDE OF KONZL; UPON CROSSING KONZL SOCAL APCH CLEARED US TO DESCEND VIA THE SEAVU1 FOR THE ILS TO RWY 24R. I WAS THE NON FLYING PLT AND CHANGED THE APCH IN THE FMC FROM THE ILS RWY 25L TO THE ILS RWY 24R. AT THE TIME OF THE CHANGE THE ACFT WAS ON AUTOPLT DESCENDING VNAV PTH; WHEN THE AIRPLANE REVERTED TO VNAV SPD DURING THE RWY CHANGE. THE CAPT AND I WERE CLARIFYING THE RWY CHANGE WITH EACH OTHER AND I WAS VERIFYING THE LEGS FOR THE TRANSITION AND APCH WHEN I THEN NOTICED THE AIRPLANE REVERTED TO VNAV SPD AND DESCENDED BELOW THE CATAW RESTRICTION OF 14000 FT OR MORE. ACFT DESCENDED AND CROSSED CATAW AT 13500 FT. THERE WAS NO INQUIRY FROM ATC NOR WAS THERE ANY TA ADVISORIES OR RESOLUTION. VNAV PTH WAS REENGAGED AND THE FLT CONTINUED WITHOUT FURTHER INCIDENT. AUTOMATION; WHEN IT WORKS WELL IS A GREAT THING; BUT HAS ITS PITFALLS AS WELL. THOSE OF US WHO FLY IN AND OUT OF LAX FREQUENTLY KNOW THAT ATC WILL CHANGE RWYS ON THIS ARR AT AN INCONVENIENT AND HIGHLY DISTRACTING TIME. BOTH PLTS NEED TO MONITOR ANY CHANGES TO RTE AND VERIFY THAT THE MODIFICATION HAS NOT CHANGED THE PATH AS WELL.

Data retrieved from NASA's ASRS site as of May 2009 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.

An air carrier received an lax seavu runway change during descent. The FMS reverted to VNAV speed as the FMS was reprogrammed. The cataw altitude constraint was missed because the crew did not see the mode reversion out of VNAV path.