A B757-200 flight crew was unable to comply with the crossing altitude restriction at pldge on the f...

Attributes
ACN	1083481
Time
Date	201304
Local Time Of Day	1201-1800
Place
Locale Reference	ZDC.ARTCC
State Reference	VA
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR FRDMM ONE
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 230 Flight Crew Total 11100 Flight Crew Type 8100
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Crossing Restriction Not Met Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

We were descending into dca via the frdmm RNAV STAR; conducting a VNAV path descent. We monitored the FMA to ensure we stayed on the VNAV path and on the vdi (vertical deviation indicator) during the descent. After passing morll; still on the correct VNAV path; we reset the altimeters at FL180 from 29.92 to 30.56. The next waypoint; pldge; is supposed to be crossed at 280 KTS between 17;000 and 15;000. Due to the large altimeter change (which increased our qnh vice qne indicated altitude by 640 ft) the very short distance between morll and pldge and the inability of VNAV to deal with the altimeter change in such a short period of time; we crossed pldge higher than 17;000. During all this; we monitored the FMA the entire time. We never left VNAV path once; yet we still crossed pldge high! Upon changing the altimeter; the vdi briefly went away; FMA stayed in VNAV path. The vdi came back after maybe 10 seconds and showed us on the correct vertical track. The speed began to slow towards 250 (no idea why [as we were] still in VNAV path). As we neared 250; it became apparent that VNAV didn't know what it was doing. We flch'd it down as quick as we could; including speed brake use; but there was no way to catch up at that point.

Original NASA ASRS Text

Title: A B757-200 flight crew was unable to comply with the crossing altitude restriction at PLDGE on the FRDMM RNAV STAR into DCA when the switch from QNE to QNH passing FL180 increased their indicated altitude by 640 FT.

Narrative: We were descending into DCA via the FRDMM RNAV STAR; conducting a VNAV Path descent. We monitored the FMA to ensure we stayed on the VNAV PATH and on the VDI (vertical deviation indicator) during the descent. After passing MORLL; still on the correct VNAV PATH; we reset the altimeters at FL180 from 29.92 to 30.56. The next waypoint; PLDGE; is supposed to be crossed at 280 KTS between 17;000 and 15;000. Due to the large altimeter change (which increased our QNH vice QNE indicated altitude by 640 FT) the very short distance between MORLL and PLDGE and the inability of VNAV to deal with the altimeter change in such a short period of time; we crossed PLDGE higher than 17;000. During all this; we monitored the FMA the entire time. We never left VNAV PATH once; yet we still crossed PLDGE high! Upon changing the altimeter; the VDI briefly went away; FMA stayed in VNAV PATH. The VDI came back after maybe 10 seconds and showed us on the correct vertical track. The speed began to slow towards 250 (no idea why [as we were] still in VNAV PATH). As we neared 250; it became apparent that VNAV didn't know what it was doing. We FLCH'd it down as quick as we could; including speed brake use; but there was no way to catch up at that point.

Data retrieved from NASA's ASRS site as of July 2013 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.

A B757-200 flight crew was unable to comply with the crossing altitude restriction at pldge on the frdmm RNAV STAR into dca when the switch from qne to qnh passing FL180 increased their indicated altitude by 640 ft.