When the left IRS failed the flight crew of a B737NG was surprised the qrc did not direct them to se...

Narrative:

Left IRS failure.'unable requested navigation performance - rnp' alert was first indication of possible navigational problems. Autopilot disengaged simultaneously as the IRS fail light illuminated on the left IRS. Completed the IRS failure QRH checklist; establishing a platform in the 'att' mode on left IRS (IRS fault light extinguished). Heading was manually entered and updated in the FMC. LNAV was not accurate (cleared direct lmn) tracking to waypoint. Navigated via heading select mode; VOR; and center vectors. Per fom 'equipment failures in rvsm airspace' it did not appear that this failure would prohibit continued cruise at FL370. Both primary altimeters were operating and altitude hold functions of both autopilots were regained. Dispatch disagreed; so descent to FL280 occurred shortly thereafter with ATC assistance. Captain's ADI was unreliable during the approach; so both on 'right' (IRS) was selected during the visual approach; circle runway xxl ZZZ. Approximately 400 ft AGL; pws aural warning 'windshear; windshear; windshear' (no associated warning light) on final was disregarded. At approximately 90 KIAS on landing rollout; stick shaker initiated for about 6-8 seconds. Good question! 2 comments/questions: 1) I found my IRS/FMC knowledge less than optimal for this type of situation. 2) the QRH checklist does not direct the pilot to select the valid IRS. If the fault light extinguishes; as it did in this case; 2 steps remain on the QRH checklist: 1) CDU or ISDU...enter heading; 2) autopilot approach mode...do not engage; stop. If we assessed the problem and completed the checklist correctly; why does it not direct the pilot to select the valid IRS?

Original NASA ASRS Text

Title: When the left IRS failed the flight crew of a B737NG was surprised the QRC did not direct them to select the right IRS. Encountered several failure mode indications during remainder of the flight.

Narrative: Left IRS failure.'Unable Requested Navigation Performance - RNP' alert was first indication of possible navigational problems. Autopilot disengaged simultaneously as the IRS Fail light illuminated on the left IRS. Completed the IRS failure QRH checklist; establishing a platform in the 'ATT' mode on left IRS (IRS fault light extinguished). Heading was manually entered and updated in the FMC. LNAV was not accurate (cleared direct LMN) tracking to waypoint. Navigated via heading select mode; VOR; and Center vectors. Per FOM 'equipment failures in RVSM Airspace' it did not appear that this failure would prohibit continued cruise at FL370. Both primary altimeters were operating and altitude hold functions of both autopilots were regained. Dispatch disagreed; so descent to FL280 occurred shortly thereafter with ATC assistance. Captain's ADI was unreliable during the approach; so both on 'R' (IRS) was selected during the visual approach; circle Runway XXL ZZZ. Approximately 400 FT AGL; PWS aural warning 'Windshear; Windshear; Windshear' (no associated warning light) on final was disregarded. At approximately 90 KIAS on landing rollout; stick shaker initiated for about 6-8 seconds. Good question! 2 comments/questions: 1) I found my IRS/FMC knowledge less than optimal for this type of situation. 2) The QRH checklist does not direct the pilot to select the valid IRS. If the fault light extinguishes; as it did in this case; 2 steps remain on the QRH checklist: 1) CDU or ISDU...enter heading; 2) Autopilot Approach Mode...Do not engage; stop. If we assessed the problem and completed the checklist correctly; why does it not direct the pilot to select the valid IRS?

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	827659
Time
Date	200903
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Flight Dynamics Navigation and Safety
Person 1
Function	Captain Pilot Flying
Experience	Flight Crew Last 90 Days 81 Flight Crew Type 8000
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

When the left IRS failed the flight crew of a B737NG was surprised the qrc did not direct them to select the right IRS. Encountered several failure mode indications during remainder of the flight.