The Boeing 777 utilizes a complex series of systems and triggers to progress through takeoff, climb, cruise, descent, landing, and rollout. The first step of the B777 automated takeoff is to set throttles and begin rolling. Autothrottles take over as speed increases. As the aircraft accelerates above 100 knots indicated airspeed (KIAS), the flight computer records the barometric altitude which will feed the vertical navigation (VNAV) system when it is engaged. The pitch command will rotates the aircraft. At 50 feet the lateral navigation (LNAV) system engages, at 400 feet the VNAV engages. (B777, nd).
The landing portion of the flight begins with runway alignment. The B777 system is capable of correcting for crosswinds and crabbing as necessary. At 50 feet radio altitude the system will begin the flare maneuver. Once the aircraft is less than two feet radio altitude the system will engage the rollout mode which allows for touchdown. The autopilot will perform rudder and nose gear steering during rollout (B777, nd). All of these modes and systems require complex interoperability among many systems to accomplish a safe flight.
The Boeing/Insitu ScanEagle uses a much more rudimentary automated takeoff and landing system. The ScanEagle is “catapult launched from a pneumatically operated wedge launcher with a launch velocity of 25m/s [55 mph]” (Naval-Technology, 2016). Once the ScanEagle is airborne it is commanded by a 900 MHz UHF datalink. The ScanEagle can fly autonomously back to home station where“the patented SkyHook recovery system is used for retrieval. SkyHook catches the aircraft’s wingtip with a rope that hangs from a 50-foot-high (15-meter-high) boom” (Boeing, nd). Essentially the landing is a controlled crash where the aircraft is snagged out of the sky by the SkyHook. The ScanEagle does not have any landing gear.
Each of the automated takeoff and landing systems these aircraft use is appropriately suited for its mission. The $100,000 unmanned ScanEagle is disposable when compared to $320 million Boeing 777 with up to 365 passengers (Ausick, 2014). The ScanEagle’s failsafe actions are to crash. It does not have an alternative to the SkyHook recovery. The B777 automated takeoff and landing system, however, can be interrupted at any portion of the flight profile. Additionally portions of the automated system can be disengaged such as the VNAV, LNAV, or autothrottle. One limitation of the automated system is in contingency situations such as Flight 1549 where Capt Sullenberger landed his Airbus A320 on the Hudson River following a bird strike during takeoff. The automated system does not have the situational awareness or alternative thinking and reactions of a human. In this case a human pilot is necessary for safe operation.
When it comes to automated takeoff and landing the operation of the system is proportional to the aircraft operating it. The micro-UAS ScanEagle is actually better served through simplicity. This makes the system must more transportable and usable for forward deployed troops. The B777, however, must operate in varying environmental conditions and airports. More than that it is responsible for the safe transportation of its passengers and therefore requires a much more complex system to ensure safety.
References
Ausick, P. (2014, June 27). 24/7 Wall St. Retrieved from Why a Boeing 777-300ER Costs $320 Million: http://247wallst.com/aerospace-defense/2014/06/27/why-a-boeing-777-300er-costs-320-million/
Boeing. (nd). ScanEagle Unmanned Aerial Vehicle. Retrieved from Historical Snapshot: http://www.boeing.com/history/products/scaneagle-unmanned-aerial-vehicle.page
Naval-Technology. (2016). Naval-Technology. Retrieved from ScanEagle, United States of America: http://www.naval-technology.com/projects/scaneagle-uav/
Walker, R. (2015, March 28). The Globalist. Retrieved from When Do Planes Crash: http://www.theglobalist.com/when-do-planes-crash/
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