The flight crew of a B737 was surprised when their autoflight system began a descent on an RNAV STAR...

Attributes
ACN	1047366
Time
Date	201211
Local Time Of Day	1801-2400
Place
Locale Reference	DCA.Airport
State Reference	DC
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Make Model Name	B737 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 Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 15500 Flight Crew Type 750
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance

Narrative:

While descending on [one of] the complicated RNAV arrival into dca; the captain (pilot flying) missed a crossing altitude on the arrival. At the moment I was reviewing my chart for information when I heard the captain declare 'why did it do that'. After the autoflight system had descended 400 ft some two miles early he disconnected the autopilot and regained the altitude.a major contributing factor for this altitude deviation; I believe; is that these new RNAV arrivals into dca are overly complicated. Another issue could also be rest; as this was the last leg after flying 5 days in a row with much disrupted sleep and early mornings.

Original NASA ASRS Text

Title: The flight crew of a B737 was surprised when their autoflight system began a descent on an RNAV STAR into DCA prior to complying with the crossing restriction at their active waypoint.

Narrative: While descending on [one of] the complicated RNAV arrival into DCA; the Captain (pilot flying) missed a crossing altitude on the arrival. At the moment I was reviewing my chart for information when I heard the Captain declare 'why did it do that'. After the autoflight system had descended 400 FT some two miles early he disconnected the autopilot and regained the altitude.A major contributing factor for this altitude deviation; I believe; is that these new RNAV arrivals into DCA are overly complicated. Another issue could also be rest; as this was the last leg after flying 5 days in a row with much disrupted sleep and early mornings.

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.

The flight crew of a B737 was surprised when their autoflight system began a descent on an RNAV STAR into dca prior to complying with the crossing restriction at their active waypoint.