The flight crew of a C560XL departed their assigned altitude prematurely when the FMS VNAV function failed to comply with the crossing restrictions programmed via the JAIKE RNAV STAR to TEB.
Synopsis
The flight crew of a C560XL departed their assigned altitude prematurely when the FMS VNAV function failed to comply with the crossing restrictions programmed via the JAIKE RNAV STAR to TEB.
Narrative
We were at an assigned altitude of 13;000 FT; airspeed was 280 KTS and we were approximately 18 DME south of Ilene Waypoint on the Jaike 2 RNAV arrival. 13;000 FT was the crossing altitude for Ilene fix. New York Center cleared us to descend via the Jaike 2 RNAV arrival. I had verified the altitudes and airspeed restrictions on the arrival on the FMS prior to engine start. Before we started our descent my copilot and I both reviewed the altitude and airspeed requirements of the RNAV arrival. The flying pilot set the flight director up for a VNAV descent and I placed 7;000 FT; the lowest altitude on the arrival; in the altitude alerter.When the flying pilot activated the VNAV button on the flight director the aircraft immediately pitched to 1;800 to 2;000 FT descent angle. I directed the flying pilot to stop the descent and return to 13;000 FT. We had descended to about 12;450 FT before we established the climb. We then proceeded to descend via the approach using VS function and setting only the next required altitude in the altitude alerter. The event lasted about 15 seconds from initial descent to return to 13;000 FT.My experience with the autopilot and FMS of the XL has shown the systems to be very inconsistent. I will not put any altitudes beyond the next altitude on the next fix in the altitude alerter during RNAV arrivals. I ALWAYS monitor what the autopilot is doing. The abruptness of the descent was; even for the XL; unexpected. The performance page had been set up according to SOP and reviewed before flight. I believe the autopilot attempted to attain 300 KTS by descending and ignored the altitude requirements in the FMS.
Second reporter narrative
I selected 7;000 FT in the altitude alerter; as that was the lowest altitude on the arrival; and selected the VNAV function and 'FMS' function. These extra steps are required on the XL as opposed to the XLS which requires input of the altitude then simply pushing the 'VNAV' function on the flight director.I have no idea what I did wrong. The pilot monitoring and myself both observed my input to the flight director and neither one of us could come up with a reason why the plane did what it did.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.