The DC-9 is equipped with the Sperry SP-50 Automatic Flight Control System (AFCS), which is a gyroscopically controlled electromechanical system. The DC-9 is an old school aircraft and the autopilot installed in this aircraft is very much old school too. If you are used to flying with modern autopilots, you will find that this autopilot works a bit differently than the other autopilots you may be familiar with.
The whole point of having an autopilot installed in an aircraft is to reduce the workload on the flight crew and to provide improved flight comfort and stability. In an old aircraft like the DC-9, where the level of automation is relatively low compared to newer modern aircraft, you will find that this is a very welcome feature. Use the autopilot to stay ahead of the aircraft.
Although you will find the autopilot to be a helping hand, it won’t give you as much help as you might be used to from other newer types of autopilots. Take for example a common feature in modern autopilots such as flight level change. There is no such thing in the DC-9. How about automatic level off at the preselected altitude then? Sorry, you’re going to have to do that yourself.
When you want to climb to a higher altitude, you simply set the vertical speed, pitch attitude or speed/mach hold and off you go. Once you reach your target altitude, you have to manually level off. And yes, you will have to monitor the altimeter closely during the climb. If you don’t, you are going to shoot right through that altitude and the wrath of the ATC will rain down upon you. Or maybe not.
Actually, there is some help available. You can dial in your target altitude on the Altitude Alerter. When you approach your target altitude, the Altitude Alerter will beep and flash a light at you to indicate you are approaching the target altitude. However, the Altitude Alerter will not level off the aircraft for you. You still need to take control and manually level off the aircraft.
So, how about auto throttle? Does the DC-9 come with an auto throttle system? Surprisingly, yes! That’s the good news. The bad news; Again it doesn’t quite work the way you might expect it to. Actually, most likely you have never seen an auto throttle system like this before. You might expect the auto throttle system to maintain a set airspeed or mach number selected by the flight crew. No. That’s not how this one works at all.
The DC-9 auto throttle system was designed for use during the approach phase only. Basically, when you are flying down the ILS or descending on a non-precision approach, that’s when you can use the auto throttle system. When engaged, the auto throttle system will maintain the computed approach reference speed (VREF), which is based on aircraft weight and flap setting. You don’t get to select the speed at which the auto throttle system will control the aircraft, the computer does. You do not use this auto throttle system for climbout, cruise or any other phase of flight.
It may not seem as though the autopilot in this aircraft gives you much help at all. But I guarantee you, you will appreciate all the help you can get when the heat is on; “There I was, blasting down the runway past V1, when all of a sudden…”.