|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1801 To 2400|
|Locale Reference||atc facility : cvi|
|Altitude||msl bound lower : 33000|
msl bound upper : 34000
|Controlling Facilities||artcc : zdc|
|Operator||common carrier : air carrier|
|Make Model Name||Large Transport, Low Wing, 2 Turbojet Eng|
|Navigation In Use||Other |
|Flight Phase||descent other|
|Route In Use||enroute airway : zdc|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : atp|
|Experience||flight time last 90 days : 240|
flight time total : 13000
|Function||flight crew : first officer|
|Qualification||pilot : instrument|
pilot : commercial
|Anomaly||altitude deviation : crossing restriction not met|
altitude deviation : undershoot
non adherence : clearance
other anomaly other
|Independent Detector||other controllera|
|Resolutory Action||none taken : anomaly accepted|
|Air Traffic Incident||Pilot Deviation|
The aircraft was an large transport en route from mia to dca. Deviating around thunderstorms, using the offset feature of the LNAV. Given a clearance to cross 40 mi south of cvi at FL330. The fix was created and entered into the VNAV on a crossing restriction. The T/D point was created by the computer. When approximately 70 mi out, the offset was cancelled and the plane started back to the original course. When approximately 3 mi south of the 40 mi fix (according to the RNAV) the center called and asked why we were not level. The IRU or RNAV position still showed us with 2 1/2 mi to go. Then center insisted that we were 40 mi out of civ. The basic problem with this is that on the large transport, all dscnts and climbs are based upon IRS based position generation of the IRU's. In this case, the IRU's position showed 3.1 mi to go before the fix. Also, the VNAV was working the descent. Neither pilot had any position readout from the VOR at cvi because the VOR's were in automatic and the FMC's determined VOR tuning.
Original NASA ASRS Text
Title: ADVANCED TECHNOLOGY ACR MLG UNDERSHOT CROSSING RESTRICTION ON DESCENT.
Narrative: THE ACFT WAS AN LGT ENRTE FROM MIA TO DCA. DEVIATING AROUND TSTMS, USING THE OFFSET FEATURE OF THE LNAV. GIVEN A CLRNC TO CROSS 40 MI S OF CVI AT FL330. THE FIX WAS CREATED AND ENTERED INTO THE VNAV ON A XING RESTRICTION. THE T/D POINT WAS CREATED BY THE COMPUTER. WHEN APPROX 70 MI OUT, THE OFFSET WAS CANCELLED AND THE PLANE STARTED BACK TO THE ORIGINAL COURSE. WHEN APPROX 3 MI S OF THE 40 MI FIX (ACCORDING TO THE RNAV) THE CENTER CALLED AND ASKED WHY WE WERE NOT LEVEL. THE IRU OR RNAV POS STILL SHOWED US WITH 2 1/2 MI TO GO. THEN CENTER INSISTED THAT WE WERE 40 MI OUT OF CIV. THE BASIC PROB WITH THIS IS THAT ON THE LGT, ALL DSCNTS AND CLBS ARE BASED UPON IRS BASED POS GENERATION OF THE IRU'S. IN THIS CASE, THE IRU'S POS SHOWED 3.1 MI TO GO BEFORE THE FIX. ALSO, THE VNAV WAS WORKING THE DSCNT. NEITHER PLT HAD ANY POS READOUT FROM THE VOR AT CVI BECAUSE THE VOR'S WERE IN AUTO AND THE FMC'S DETERMINED VOR TUNING.
Data retrieved from NASA's ASRS site as of August 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.