From directional control to changes in altitude, an aircraft autopilot system can control many aspects of the flight, aiding the pilot when necessary, as well as making the trek smooth and efficient. Some may be surprised to know that aircraft can even control and execute a landing, though it is very uncommon. Less than 1 in 100 commercial airliner flights are ever landed through autopilot, and it is often reserved for times where visibility is extremely poor. Nevertheless, it is something that many planes are capable of doing, and it can be a very smooth and safe operation due to the expertise of pilots. In this article, we will discuss how autopilot is able to conduct landings by itself.

When the pilot approaches the airport for a standard landing, autopilot is often used as far as when the plane is a few miles from the landing strip and it becomes visible. From then, pilots disable autopilot and execute the landing themselves, ensuring that they are able to accommodate for any change or traffic that an autopilot system cannot adapt to. Sometimes, however, when there is a storm or heavy fog, visibility may be so short as to make manual landing extremely unsafe, or even impossible.

When an aircraft readies for autopilot landing, multiple controls and equipment have to be set. As the aircraft approaches the landing strip, pilots are attentive for any possible red flag or problem so that they may take immediate control. To ensure safe landings through autopilot, pilots have to undergo training every six months. Some of this training involves pilots going through simulations that put them through any possible problem to train them how to successfully navigate through them. Because of this, pilots are always at the ready to respond to anything during their landing.

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As a plane descends and prepares for landing, it conjures an incredible amount of force around it. Planes are typically traveling at about 200 miles per hour when touching down on the runway; thus, they require a superb braking system. Even when idle, thrust is produced and travels forward as it acts against the deceleration systems. The braking system on aircraft are sufficient enough to stop most aircraft, yet in case of emergency, another deceleration method is needed for safety purposes and to prolong the longevity of the brakes.

An efficient modus operandi to achieve this need is thrust reversal. Thrust reversal is the process in which the engine of the aircraft temporarily redirects the thrust forward instead of backward. The reversal of the thrust counteracts the forward travel of the aircraft and assists in deceleration. Thrust reversal has also been used to reduce the airspeed mid-flight. Reverse thrust can be generated by a reversible pitch propeller, or on a jet engine by a target reverser.

Reverse thrust is usually enacted immediately after the plane touches down when aerodynamic lift limits the effectiveness of the brakes. It is always operated manually by the pilot, utilizing thrust levers to maintain full control. Although thrust reversal is a supplemental tool in bringing the aircraft to a stop, regulations dictate that an aircraft must be able to land regardless of the use of thrust reversal.

There are several different methods of obtaining reverse thrust on aircraft. The first one involves clamshell type deflector doors to implement a reversal of the gas exhaust stream. Another method involves utilizing external doors to reverse the exhaust flow. The last process involves fan engines using blocker doors that reverse the airflow.

Once the speed of the aircraft has slowed, it is crucial to shut down the reverse thrust to prevent the reversed air from lifting debris in front of engine intakes. If debris is ingested, it can cause severe damage. A powerback is when reverse thrust is used to move an aircraft away from the gate. Reverse thrust performs optimally when the aircraft is at higher speeds.

Smaller aircraft don’t require thrust reversal systems except in specialized situations.

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The average passenger aircraft has upwards of 1,000 various aircraft cable bundles installed within its structure. The wiring and cable assemblies serve integral tasks including flight control, data bus, fireproof redundancy, and more. Two of those cable systems that are imperative to avionics are flight control cables and data bus cables.  

Flight control systems manage a variety of monitoring and actuating tasks. These cables stretch from the cockpit to control surfaces within the airframe. They are typically stainless-steel wiring bundles that are coated in a black vinyl casing. Stainless steel is able to withstand greater temperature variations than the mostly aluminum frame of an aircraft but are still affected by the thermal contractions of the airframe.

In order to maintain efficient communication with control surface actuators and remain reliable under the many stressors encountered during a flight cycle, flight control cables are assembled using a pulley system. When a pilot actuates a control, a cable is rotated around the pulleys like a large steel belt. Each system is spring loaded, which helps account for slack that occurs when the aircraft encounters drastic temperature changes.

While flight control cables interact with actuators, data bus cables transmit digital signals between sensors and their corresponding display devices. A standard commercial airplane has 150 to 300 ft. (around 200 km) of this type of cable alone. Data bus cable structure often consist of a shielded “twisted pair” cable that is grounded at each end, and at every junction in the assembly. The most commonly used data bus system in civil aviation is the ARINC 429. Created by Aeronautical Radio Inc., it is the technical avionics standard for data bus cables used in commercial aircraft. This system operates using a double helix wiring, which enables bi-directional transmission to request data and transmit data across a single cable. 

Both flight control cables and data bus cables are essential to a pilot for proper monitoring of an aircraft during its flight cycle. As technology advances, it is possible we will see steel wiring replaced with fiber optics technology. The lighter, more reliable, cables have a lower electromagnetic field (EMF) and are notably more affordable. Newer airplanes such as the Airbus A380 and Boeing 787, have already incorporated fiber optic cables into some part of their avionics systems. As older aircraft phase out, it is likely we will see fiber optics technology become the new standard for aircraft cables.

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