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A B737 flight crew descending into den on the larks arrival experiences an IRS failure that causes an autoplt hard over and pitch down just after they get a TCAS.
| Attributes | |
| ACN | 709225 |
| Time | |
| Date | 200609 |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | intersection : larks |
| State Reference | CO |
| Altitude | msl single value : 16000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : d01.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | descent : intermediate altitude |
| Route In Use | arrival star : larks 5 |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 270 flight time total : 16000 flight time type : 6000 |
| ASRS Report | 709225 |
| Person 2 | |
| Function | flight crew : first officer |
| Experience | flight time last 90 days : 70 flight time total : 17000 flight time type : 4000 |
| ASRS Report | 708876 |
| Events | |
| Anomaly | aircraft equipment problem : less severe conflict : airborne less severe non adherence : published procedure non adherence : clearance other anomaly other anomaly |
| Independent Detector | other controllera other flight crewa other flight crewb |
| Resolutory Action | flight crew : overcame equipment problem flight crew : regained aircraft control |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance ATC Human Performance Aircraft Airspace Structure |
| Primary Problem | Ambiguous |
Narrative:
Arrival in den initially was powdr 5 and was changed to larks 5. We received clearance to cross larks 250 KTS/17000 ft too late. We made 17000 ft but the speed was 290 KTS. Next clearance was descend to 14000 ft speed 210 KTS. A few seconds later ATC said stop your descent; stop your descent. We stopped at 16000 ft; next was turn left heading 350 degrees. I start turning and TCAS went off. I follow the TCAS and turn right 20 degrees to avoid traffic next to us at 10 O'clock position. Traffic was at 16500 ft descending; radio frequency was saturated; everybody stepping on each other; we did not have a chance to tell ATC what happened. We got the frequency change and at this time left IRS failed with autoplt on. We experienced a hard over and aggressive nose dive. I disconnected autoplt and autothrottle and recovered the airplane. I lost eadi and ehsi; I told first officer could you xfer your picture to my side; he said I sure would like to help but I just lost mine. At this moment standby instruments were the only thing I could use. Approach and landing were uneventful. After we parked we called ATC. It was a mutual discussion; we agreed that a lot happened in just a few mins; the only thing was the outcome; no damage; nobody got hurt.
Original NASA ASRS Text
Title: A B737 FLT CREW DSNDING INTO DEN ON THE LARKS ARR EXPERIENCES AN IRS FAILURE THAT CAUSES AN AUTOPLT HARD OVER AND PITCH DOWN JUST AFTER THEY GET A TCAS.
Narrative: ARR IN DEN INITIALLY WAS POWDR 5 AND WAS CHANGED TO LARKS 5. WE RECEIVED CLRNC TO CROSS LARKS 250 KTS/17000 FT TOO LATE. WE MADE 17000 FT BUT THE SPD WAS 290 KTS. NEXT CLRNC WAS DSND TO 14000 FT SPD 210 KTS. A FEW SECONDS LATER ATC SAID STOP YOUR DSCNT; STOP YOUR DSCNT. WE STOPPED AT 16000 FT; NEXT WAS TURN L HDG 350 DEGS. I START TURNING AND TCAS WENT OFF. I FOLLOW THE TCAS AND TURN R 20 DEGS TO AVOID TFC NEXT TO US AT 10 O'CLOCK POS. TFC WAS AT 16500 FT DSNDING; RADIO FREQ WAS SATURATED; EVERYBODY STEPPING ON EACH OTHER; WE DID NOT HAVE A CHANCE TO TELL ATC WHAT HAPPENED. WE GOT THE FREQ CHANGE AND AT THIS TIME L IRS FAILED WITH AUTOPLT ON. WE EXPERIENCED A HARD OVER AND AGGRESSIVE NOSE DIVE. I DISCONNECTED AUTOPLT AND AUTOTHROTTLE AND RECOVERED THE AIRPLANE. I LOST EADI AND EHSI; I TOLD FO COULD YOU XFER YOUR PICTURE TO MY SIDE; HE SAID I SURE WOULD LIKE TO HELP BUT I JUST LOST MINE. AT THIS MOMENT STANDBY INSTS WERE THE ONLY THING I COULD USE. APCH AND LNDG WERE UNEVENTFUL. AFTER WE PARKED WE CALLED ATC. IT WAS A MUTUAL DISCUSSION; WE AGREED THAT A LOT HAPPENED IN JUST A FEW MINS; THE ONLY THING WAS THE OUTCOME; NO DAMAGE; NOBODY GOT HURT.
Data retrieved from NASA's ASRS site as of January 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.