B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 126; Flight Crew Total 12536; Flight Crew Type 9068
Situational Awareness; Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action
Aircraft; Human Factors
VEPLI1B RNAV arrival into WSSS. The STAR has several altitude and speed restrictions and First Officer began the descent on VNAV to comply with the restrictions on the arrival procedure. ATC clearance was to FL240. Descending through FL300; the aircraft began to accelerate above the FMS commanded descent speed of 290 KTS. When the aircraft continued to accelerate in the descent through 320 knots; and the First Officer reacted by opening the speed window and speed intervened by selecting a speed again of 290 KTS. The aircraft did not respond to the commanded speed; in fact it continued to lower the nose and accelerate; at which time I verbalized that the aircraft might overspeed. First Officer dialed in a further speed reduction in the window of 250 KTS; but the airspeed did not slow as it should; it continued to accelerate. Overspeed warning occurred and First Officer disengaged the autopilot and leveled the aircraft off at FL250 and then continued the descent to FL240. During the recovery the airspeed reached approximately 340 KTS (about 15 KTS above Vmo).Once the speed was again under control; First Officer reengaged the autopilot; but did not reengage VNAV and used FLCH and vertical speed for the remainder of the arrival. This exceedance was inadvertent. Opening the airspeed window and reducing commanded airspeed in VNAV should have pitched the nose further up thereby reducing airspeed; but did not for some explainable reason. Regardless; in the future; I will be more vigilant in actually verbalizing that the autopilot should be disengaged sooner so as to prevent/minimize overspeed.
[Report narrative contained no additional information.]
B767-300 flight crew experienced increasing airspeed while descending on the VEPLI1 RNAV arrival to WSSS. Speed intervene had no apparent effect; but the autopilot was not disengaged until the overspeed warning sounded ultimately being exceeded by 15 knots before slowing.