Narrative:

Since their introduction; I have flown both CAVLR2 arrival into iad and the CAPSS1 arrival into dca several times. I have seen the aircraft consistently struggle to meet both the crossing and speed restrictions without very large speed excursions. It appears that the aircraft pitches up to make the 250 knot speed restriction and then dives to make the 10;000 feet altitude restrictions. On several occasions; we have had to disconnect the autopilot and intervene in order to prevent an aircraft overspeed.on a few occasions; I have attempted to preclude this situation by placing more conservative 'hard' altitudes (in compliance with the speeds and altitudes on the arrival) at several or all of the fixes in the profile. However; the aircraft still executes a 'pitch up and dive' maneuver in order to fly the profile. Recovery from these events has typically happened during an extremely high workload phase of flight.it is apparent that the combination of a steep profile and limited distance for deceleration are too extreme for the FMC to fly; even in the best conditions. A weather event or any sort of tailwind would make these arrivals unthinkable.the cavlr and capss arrivals need to be revised to reflect how the FMC software actually attempts to fly these profiles.

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Original NASA ASRS Text

Title: B737-800 Captain reported the CAVLR2 arrival into IAD and the CAPSS1 arrival into DCA are not flown properly by his aircraft's autoflight system.

Narrative: Since their introduction; I have flown both CAVLR2 Arrival into IAD and the CAPSS1 Arrival into DCA several times. I have seen the aircraft consistently struggle to meet both the crossing and speed restrictions without very large speed excursions. It appears that the aircraft pitches up to make the 250 knot speed restriction and then dives to make the 10;000 feet altitude restrictions. On several occasions; we have had to disconnect the autopilot and intervene in order to prevent an aircraft overspeed.On a few occasions; I have attempted to preclude this situation by placing more conservative 'hard' altitudes (in compliance with the speeds and altitudes on the arrival) at several or all of the fixes in the profile. However; the aircraft still executes a 'pitch up and dive' maneuver in order to fly the profile. Recovery from these events has typically happened during an extremely high workload phase of flight.It is apparent that the combination of a steep profile and limited distance for deceleration are too extreme for the FMC to fly; even in the best conditions. A weather event or any sort of tailwind would make these arrivals unthinkable.The CAVLR and CAPSS arrivals need to be revised to reflect how the FMC software actually attempts to fly these profiles.

Data retrieved from NASA's ASRS site 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.