The UK’s Air Accidents Investigation Branch (AAIB) released a report in early June detailing how a crew approaching Scotland’s Glasgow Airport (EGPF) flew through an assigned altitude by inadvertently activating the “go-around” button on a Beechcraft King Air 200 just as the autopilot was about to capture a preset altitude. The ensuing confusion during the nighttime IMC incident was compounded by the specific cockpit setup of the King Air they were flying, which was different from the version they normally operated.
Vectored to the ILS 23 at Glasgow, the first officer acted as the flying pilot while using the autopilot. Upon receiving a descent clearance to 3,500 feet and to begin slowing the aircraft, the pilot pulled off some power, causing the gear horn to sound. In the King Air the pilot was accustomed to flying, the “horn silence” button was located on the left power lever.
On this particular King Air, that same position held the go-around button. When the pilot pressed it, the flight director gave him a “fly-up” indication and previous automation commands were lost. The captain tried unsuccessfully to re-engage the automation while also silencing the gear horn when he noticed the aircraft was already descending below 3,000 feet at a steep rate.
The ground proximity warning system chimed in with a “terrain, terrain, pull up” warning because the aircraft, now at 2,273 feet msl, was only 1,484 feet above the ground. The captain called for full power and the first officer added it as he pitched the aircraft back up to 3,500 feet.
The AAIB’s investigation discovered that both pilots normally flew an aircraft equipped with Rockwell Collins Pro Line 21 avionics, rather than the steam gauges of the incident aircraft. The flying pilot also said he was distracted by his inability to silence the gear horn. On the Pro Line 21-equipped King Air, the gear horn silence button is located on the left side of the left power lever just beneath the go-around button. The subtle difference was that the GA button on the Pro Line 21 aircraft is located in a recess on the left side of that same power lever.