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Distraction of unusual performance of the automation of a B717 during an ILS approach results in a small diversion from altitude.
| Attributes | |
| ACN | 527980 |
| Time | |
| Date | 200110 |
| Day | Mon |
| Place | |
| Locale Reference | airport : atl.airport |
| State Reference | GA |
| Altitude | msl bound lower : 2400 msl bound upper : 2700 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tower : zzz.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B717 (Formerly MD-95) |
| Flight Phase | descent : approach |
| Route In Use | approach : instrument precision arrival : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : cfi pilot : atp |
| Experience | flight time last 90 days : 200 flight time total : 6000 flight time type : 800 |
| ASRS Report | 527980 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other spatial deviation |
| Resolutory Action | controller : issued alert flight crew : overcame equipment problem flight crew : overrode automation |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Aircraft |
Narrative:
From lga to katl WX forecast good. A fog layer developed at katl requiring us to hold. We were within 5 min of having to go to our altitude. The WX came up and we took vectors for the runway 9 right ILS at atl. Part of the vector was to descend to 2700 ft MSL, this coincided with localizer capture, we also were told to slow to 160 KTS. During this time we had an intermittent warning of the ILS untunable. As we prepared to take action the ILS tuned without further incident (supposed to tune within 25 NM). The problem was that for some reason during the localizer capture, slow down and level off, the autoplt and autothrottles were slow to capture the altitude. This is very unusual. At 200 ft deviation we had an altitude alert from the aircraft. The captain disconnected the autoplt and began to correct. At this time ATC informed us that we looked low. We responded and immediately corrected. I believe we got 300 ft low during the final vector, the only conflict being terrain clearance. We were VMC above a 200 ft thick fog layer. A very automated aircraft is like having a 3RD pilot and by design allows for more situational awareness and eyes outside the cockpit. When the computer does a flawless job 99 times out of 100, you are convinced it will do it every time. However once again proven, at the worst possible moment, murphy's law, or the engineer/programmer will help make your day! Also a factor, this was a stand up with 5 hours sleep.
Original NASA ASRS Text
Title: DISTRACTION OF UNUSUAL PERFORMANCE OF THE AUTOMATION OF A B717 DURING AN ILS APCH RESULTS IN A SMALL DIVERSION FROM ALT.
Narrative: FROM LGA TO KATL WX FORECAST GOOD. A FOG LAYER DEVELOPED AT KATL REQUIRING US TO HOLD. WE WERE WITHIN 5 MIN OF HAVING TO GO TO OUR ALT. THE WX CAME UP AND WE TOOK VECTORS FOR THE RWY 9 R ILS AT ATL. PART OF THE VECTOR WAS TO DSND TO 2700 FT MSL, THIS COINCIDED WITH LOC CAPTURE, WE ALSO WERE TOLD TO SLOW TO 160 KTS. DURING THIS TIME WE HAD AN INTERMITTENT WARNING OF THE ILS UNTUNABLE. AS WE PREPARED TO TAKE ACTION THE ILS TUNED WITHOUT FURTHER INCIDENT (SUPPOSED TO TUNE WITHIN 25 NM). THE PROBLEM WAS THAT FOR SOME REASON DURING THE LOC CAPTURE, SLOW DOWN AND LEVEL OFF, THE AUTOPLT AND AUTOTHROTTLES WERE SLOW TO CAPTURE THE ALT. THIS IS VERY UNUSUAL. AT 200 FT DEV WE HAD AN ALT ALERT FROM THE ACFT. THE CAPT DISCONNECTED THE AUTOPLT AND BEGAN TO CORRECT. AT THIS TIME ATC INFORMED US THAT WE LOOKED LOW. WE RESPONDED AND IMMEDIATELY CORRECTED. I BELIEVE WE GOT 300 FT LOW DURING THE FINAL VECTOR, THE ONLY CONFLICT BEING TERRAIN CLRNC. WE WERE VMC ABOVE A 200 FT THICK FOG LAYER. A VERY AUTOMATED ACFT IS LIKE HAVING A 3RD PLT AND BY DESIGN ALLOWS FOR MORE SITUATIONAL AWARENESS AND EYES OUTSIDE THE COCKPIT. WHEN THE COMPUTER DOES A FLAWLESS JOB 99 TIMES OUT OF 100, YOU ARE CONVINCED IT WILL DO IT EVERY TIME. HOWEVER ONCE AGAIN PROVEN, AT THE WORST POSSIBLE MOMENT, MURPHY'S LAW, OR THE ENGINEER/PROGRAMMER WILL HELP MAKE YOUR DAY! ALSO A FACTOR, THIS WAS A STAND UP WITH 5 HOURS SLEEP.
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.