B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP); Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Instrument
Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation - Altitude Undershoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Regained Aircraft Control; Flight Crew Overcame Equipment Problem
Aircraft
On initial climb leveling at 5;000 feet then cleared to 13;000 feet. Autopilot was engaged. Autopilot was in VNAV ALT. When cleared to 13;000; aircraft was stuck in ALT HOLD. Speed began to increase rapidly. Captain was pilot flying. I called airspeed out. Nothing he did would bring the autopilot out of ALT HOLD. He disconnected the autopilot. Speed was about 285 knots. He increased pitch and corrected airspeed. I noticed that speed window was open and indicating 148 knots. I suggested cycling flight director switches to reset MCP. This was successful and we re-automated. Flight was normal following this correction.
Speed greater than 250 knots (285 knots observed) below 10;000. On climbout with autopilot engaged; VNAV went into VNAV ALT approaching 5;000 feet (initial level off altitude on departure); 250 knots. ATC then cleared to 13;000 feet. Spun 13;000 in the ALT window and hit the button; with no effect. Meanwhile; aircraft was leveling off at 5;000 feet and accelerating! Multiple pushes of the ALT button would not get the aircraft to climb to new selected altitude. First Officer observed we were in ALT Hold with the speed window open and set to 148 knots. Autopilot was disconnected and climb initiated. In the recovery; airspeed was observed as high as 285 knots. First Officer reset both flight directors and after speed stabilized in a climb; autopilot was re-engaged. No further issues.Still cannot understand why the aircraft accelerated past 250 knots in VNAV ALT. Flight Director reset cleared the problem though. While all of this happened in a span of less than 5 seconds; I still should have disconnected the autopilot sooner.
B767-300 flight crew reported that during initial climb autopilot stuck in Altitude Hold Mode. After troubleshooting flight crew was able to regain control and flight resumed uneventfully.