Its been a few years since I operated the Metro 111. However I do remember that the best TAS at cruise power was obtained at 14,000 ft, on a ISA plus 10 day. About 250kts TAS with IAS of 210kts. At 22,000ft TAS was about 200kts with IAS of 130 kts.
Stall clean was 92kts. from memory.
The aircraft had a Stall warning system that applied forward elevator force at a speed of 1.2% V/S, to prevent a full stall.
It was common for refueling to be made to one tank. The cross flow valve could be left open during refueling and more often than not the tanks were balanced before you were ready to start for the next sector.
In-flight fuel balancing was also possible using the cross flow system ( a 2 inch pipe connecting both left and right tanks with an electric shut off valve fitted in the line, called the cross flow valve.) In-flight fuel balancing was expedited by inducing a little slip into the flight ie putting the ball out to the side you wanted the fuel to flow to. A quarter ball was ample.
However this was always accomplished with the auto pilot and yaw damper off... Otherwise the yaw damper would correct any induced yaw.
The crew on this fatal flight kept putting in more and more rudder trim until the yaw damper (trying to counteract) could not hold any longer and disengaged along with the auto pilot.
Prior to the auto-pilot disengaging, the increased drag induced by the side-slip, slowed the aircraft and the autopilot trimmed the stabiliser nose up for 11 seconds to a severe pitch up position and also the aileron trim to a right wing down to counteract the left rudder trim being put in by the flight crew.
When the autopilot disengaged the aircraft was in a very ominous trim position. The aircraft quickly snapped rolled left the nose dropped well below the horizon and the speed quickly accelerated to over 300kts. (VNE was 248kts, VMO would have been well below 248kts at FL220). The nose up stab trim position would have become nearly impossible to overcome by elevator input at that high speed and therefore imposed severely high G forces around 5gs, at which time the wings began bending up followed by the props contacting the fuselage and basically severing the flight deck from the fuselage. The wings eventually separated at the wing root and one contacted the tail and broke that from the aircraft. The aircraft fell from 19,000ft in five separate sections. This all occurred within a height loss of only 2500ft at about 6000fpm, ie in about 20 - 30 seconds.
I do know that both the stabiliser trim and rudder trim provided very powerful control inputs. The location of the ailerons (six feet inboard from wing tips) and relatively small trim tabs, did not induce very strong control forces.
The out of trim aircraft would have made recovery from the unusual attitude much more demanding in the solid IMC and dark turbulent night.
The F/O was flying pilot and very new to type, both pilots had very little experience with autopilots fitted to these aircraft, as only three of the fleet had them and they were often unserviceable.
The Captain had completed his own initial training in company whose entire fleet did not have autopilots fitted.
The report pointed to CRM issues, but I do believe that situational awareness surrounding what the A/P was doing and a lack of systems knowledge of the auto-pilot and yaw damper by both crew played a bigger part in this tragic event.
The operator has reacted by prohibiting the use of single tank refueling and the use of cross-flow in-flight, however I feel that better AFM limitations should be placed in the AFM with regards to cross-flow and autopilot use, and also a placard in the flight deck requiring the autopilot to be disengaged before using the cross-flow valve, or better still an automatic disengage of A/P when cross-flow valve is opened (not hard to do when the aircraft is electric everything). Reason being that even if side-slip is not used the fuel will still flow from one tank to the other with the cross-flow valve open, the autopilot would keep trimming for this and if left unmonitored could lead to a gross fuel imbalance situation occurring.
Sadly this is not the first incident involving Metro's using the cross-flow while the autopilot is engaged.
Fairchild the aircraft manufacture is no longer in business leaving the FAA to make any required safety airworthiness directives for this aircraft.
Finally, I thought the report was well researched before submitting.
Mangatete.