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B733 flight crew program MCP-VNAV, but aircraft system does not start descent at programmed point. Condition addressed with flight crew by ZDC.
| Attributes | |
| ACN | 510987 |
| Time | |
| Date | 200105 |
| Day | Fri |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | navaid : ihd.vortac |
| State Reference | PA |
| Altitude | msl bound lower : 24000 msl bound upper : 29000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zdc.artcc tower : iad.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| 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 : 12000 flight time type : 2400 |
| ASRS Report | 510987 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : undershoot altitude deviation : crossing restriction not met non adherence : clearance |
| Independent Detector | atc equipment other atc equipment : radar other controllera |
| Resolutory Action | none taken : detected after the fact |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
Set VNAV descent to be 100 mi south of ihd at FL240. FL240 set in MCP window, confirmed restr on legs page (built down track fix at 100 mi south of ihd). Everything was set up right, MCP 'VNAV' mode engaged (VNAV cruise). We weren't distraction, but nevertheless, missed the VNAV failing to descend. What threw me was I monitored the descent profile page and it was reading -300 FPM at runway 5R (descent required to meet restr), so when the controller asked if we were cleared to FL240, it caught us completely by surprise. No conflicts, and we hurried down to FL240. Lesson is, once again: don't trust VNAV! We use acronym 'cami' for 1) confirm, 2) activate, 3) monitor, and 4) intervene (if necessary), and we failed steps #3 and #4. I think the '-300 windows 85' FMC technology could use a big upgrade -- every time I wait for it to initiate a descent, I regret it! (Going back to vertical speed and 3:1 calculations.)
Original NASA ASRS Text
Title: B733 FLC PROGRAM MCP-VNAV, BUT ACFT SYS DOES NOT START DSCNT AT PROGRAMMED POINT. CONDITION ADDRESSED WITH FLC BY ZDC.
Narrative: SET VNAV DSCNT TO BE 100 MI S OF IHD AT FL240. FL240 SET IN MCP WINDOW, CONFIRMED RESTR ON LEGS PAGE (BUILT DOWN TRACK FIX AT 100 MI S OF IHD). EVERYTHING WAS SET UP RIGHT, MCP 'VNAV' MODE ENGAGED (VNAV CRUISE). WE WEREN'T DISTR, BUT NEVERTHELESS, MISSED THE VNAV FAILING TO DSND. WHAT THREW ME WAS I MONITORED THE DSCNT PROFILE PAGE AND IT WAS READING -300 FPM AT RWY 5R (DSCNT REQUIRED TO MEET RESTR), SO WHEN THE CTLR ASKED IF WE WERE CLRED TO FL240, IT CAUGHT US COMPLETELY BY SURPRISE. NO CONFLICTS, AND WE HURRIED DOWN TO FL240. LESSON IS, ONCE AGAIN: DON'T TRUST VNAV! WE USE ACRONYM 'CAMI' FOR 1) CONFIRM, 2) ACTIVATE, 3) MONITOR, AND 4) INTERVENE (IF NECESSARY), AND WE FAILED STEPS #3 AND #4. I THINK THE '-300 WINDOWS 85' FMC TECHNOLOGY COULD USE A BIG UPGRADE -- EVERY TIME I WAIT FOR IT TO INITIATE A DSCNT, I REGRET IT! (GOING BACK TO VERT SPD AND 3:1 CALCULATIONS.)
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.