Automatic
Takeoff and Landing
Shawn
M. Wyne
ASCI
638 – Human Factors in Unmanned Systems
Embry-Riddle
Aeronautical University
Abstract
Airplanes require a host
of skills for pilots to operate them safely. When airborne during a cruise
phase, there is larger margin of error than compared to flight near terrain. By
obvious necessity, aircraft must go near the ground at a minimum for takeoff
and landing. It is these regimes that are the most dangerous, and certainly
many mishaps that otherwise could be recovered from cause an accident. As all
aspects of flight, anything that has the potential for accidents has been
attempted to alleviate through the use of technology. Manned and unmanned
aerospace systems (UAS) both benefit from the use of automatic takeoff and
landing systems. Keywords: UAS, autoland, automatic takeoff and landing
Auto
Takeoff and Landing
Automatic takeoff and
landing systems are employed on a number of aircraft. The reason for this is
very simple. Aircraft have lots of accidents during the landing and takeoff
phases of flight. Often these accidents are the result of poor flying
conditions. Low visibility is a significantly difficult situation for a pilot
to land in, as there is minimal visual reference to align the aircraft to the
runway. A number of instruments have been developed to provide information to a
pilot for this assistance. The localizer, and instrument landing systems have
been around for decades. But even their accuracy is limited, and bad weather
may preclude even their use. The FAA defines weather minimums to allow for
particular systems to land. The worst allowable landing weather is called
Category IIIB, which means a decision height less than 50ft and runway
visibility between 150-700 feet (FAA 1999). These conditions are such than an
airliner may not actually see the runway until as few as five seconds before
touchdown. Category III weather minima basically dictates that an automatic
landing system be used; manual landing is only approved for Category II or
better weather. Another reason for using automatic takeoff or landing
procedures is for use in UAS. Datalink latency may make manual control of the
aircraft dangerous, or the control station may not even have the mechanical
controls allowing manual flight at all. All of these scenarios provide a
situation where an autopilot may be preferred, or required, to use.One aircraft that uses a variety of automatic systems is the Boeing 737-600 series and higher. The 737 actually utilizes a system capable of three different automatic approach and landing levels. A publication by Boeing by Craig, Houck, and Shomber (2003) describes the different capabilities of the aircraft. The actual autoland is the only one certified for Category IIIB operations. It works by utilizing the existing instrumentation, and details from the aircraft Flight Management System (FMS) like runway width and length, to manage aircraft parameters like pitch, engines, and brakes as appropriate. Once set up by the pilot, it is a hands-off system as long as it is working. The aircraft maintains course and decent path all the way through the flare and touchdown, applies brakes and spoilers and brings the aircraft to a complete stop. Use of reverse thrusters remains a pilot controlled item. Since it is a fail-safe design (as required by regulation), a failed system automatically reverts to manual flight. The pilot can also revert to manual flight if they choose. A second method of landing is with a GPS based landing system. This system relies on both GPS signals, and a special ground based system to provide positional information to the aircraft. This also can be reverted to manual flight, and is only approved for Category I approaches with a 200 foot decision height as of publication date. But the automatic landing is still available. There is also a third automatic approach system, but it is only for non-precision approaches and requires pilot control of altitude control and a manual decent and landing.
Another aircraft that utilizes automatic takeoff and landing capability is the General Atomics MQ-1C Gray Eagle. This aircraft utilizes automatic systems for the primary reason that the Army does not use pilots to control them. The operators are primarily sensor managers and control aircraft position by manipulating the autopilots. The takeoff and landing capability was originally enabled by use of the Tactical automatic Landing System (TALS). This is a system of ground based radars and aircraft systems that orient the aircraft’s location in relation to the runway (“TALS” n.d.). However, as that system relies on a ground element to be precisely installed and aligned, overall it was impractical for military use. The system was converted to an Automatic Takeoff and Landing System (ATLS) that is wholly onboard the aircraft. This system is strictly GPS based and therefore is more flexible. Although the system would not be at all approved for Category IIIB type approaches, the military considers it irrelevant as there are no personnel at risk in a low visibility landing, just equipment. As of 2013, the new system had surpassed 20,000 safe landings (Pocock 2013).
The success of autoland systems shows their viability in both manned and unmanned systems. However, complete reliance on such technology is not appropriate. A number of conditions or situations, both internal and external, make the autoland features unusable. Therefore, there still should be a backup method for manual landing. This is a problem for training and keeping skills up for pilots. Complacency is always an issue for automated systems, and it must be designed with human interaction in mind.
References
Craig,
R., Houck, D., and Shomber, R. (2003). 737 Approach Navigation Options. Boeing Aero Magazine. Retrieved from: http://www.boeing.com/commercial/aeromagazine/aero_22/737approach.pdf.FAA (1999, July 13). Advisory Circular 120-28D Criteria for Approval of Category III Weather Minima For Takeoff, Landing, and Rollout. US Department of Transportation Federal Aviation Administration.
Pocock, C. (2013, October 25). Improved Gray Eagle UAS Flies for 45 Hours. Retrieved from: http://www.suasnews.com/2013/10/25700/gray-eagle-completes-20000-automated-takeoffs-landings/
TALS Tactical Automatic Landing System. (n.d.). Sierra Nevada Corporation. Retrieved from http://sncorp.com/Pdfs/BusinessAreas/TALS%20Product%20Sheet.pdf
