Alt Sel Not Holding Altitude
The last couple of flights I've had a problem with selected altitude not holding once achieved. Yesterday (short 'hop' from Yeovilton to Exeter) I entered custom waypoints and preset 4000 in ALT SEL. On climbout, and achieving 4000 (with the audible 1000 to go 'bong') the altitude began to decay. I had moved condition levers to 900 and retarded throttles to maintain 240kts but airspeed started creeping up. Dreadful admission, but that was what alerted me to the slow descent. Any ideas, anyone?