Recent accident investigations have focused on how pilots used the automated systems they are surrounded with. Here’s a quick rundown of the systems available on most large airliners today and what they are used for.
Autopilot: The autopilot is the system that actually moves the aircraft flight controls. Autopilots come with a variety of different capabilities and settings depending on the aircraft and the complexity of it’s flight profile. Because the autopilot controls the aircraft flight profile, every other automated system is controlled by it.
Most airline autopilots are extremely complex in operation. They can provide a variety of flight functions depending on the mode of flight that the aircraft is in. They can climb and descend at selected rates, airspeeds, and angles. They can follow navigational beacons and GPS signals from point-to-point along a route. They can hold headings and bank angles as desired. Many other features are available depending on the aircraft and its manufacturer.
Autopilots are used on nearly every flight. Autopilots reduce pilot workload, allowing them to focus their attention on more important matters such as avoiding thunderstorms, calculating aircraft performance, fuel management, and more. Autopilots also increase passenger comfort (trust me on this one).
Auto-throttle: The auto-throttle system on modern airliners controls engine thrust to ensure that the aircraft is at the desired speed for it’s flight profile.
During takeoff, the auto-throttle can maintain takeoff thrust, during approach it can ensure that the aircraft descends at an appropriate airspeed. The auto-throttle can be set to maintain either a preset speed, or automatically programmed speeds.
Just like autopilots, the auto-throttle functions are very complex and dependent on the manufacturer. Auto-throttles are normally only seen on commercial aircraft flown at major airlines.
Auto-land: The auto-land function is a combination of autopilot and auto-throttle which allows the aircraft to land itself following the completion of a highly precise approach.
These systems are the height of complexity and require constant monitoring by the pilots. Auto-land is generally only used when the visibility at the airport is so low that the pilot may not be able to safely take control of the aircraft after seeing the runway.
Because most landings using auto-land are in poor weather, many restrictions are placed on their use. The winds must be below a certain speed, the runway surface must have proper traction, and many other factors specific to each system.
Contrary to popular belief, auto-land is used very rarely.
First, it requires intense monitoring by the pilots to ensure that the system is functioning properly.
Second, the auto-land feature requires very specific ground based navigational equipment to ensure that the aircraft is on a proper approach path. Not all airports have this capability.
Third, complex operations at busy airports often require flight profiles that would not be acceptable to the auto-land system and therefore require the pilot to fly the approach anyway. All of that aside, pilots enjoy flying, and landing is one of the best parts.
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