Manned and Unmanned Automatic Takeoff and Landing Capabilities
Brief Overview
There is a distinct importance of automated
takeoff and landings for both manned and unmanned aircraft from a performance
and safety perspective. Affording a UAV operator or pilot with the opportunity
to have a machine interface reduce workload and improve flight path control
during difficult weather conditions can have great advantages (United Stated
General Accounting Office, 1986). However, if the aircraft is in a critical
stage of flight such as takeoff and landing, regardless of the automation
level, a pilot should always be monitoring for changing conditions and
potential system abnormalities.
For this assignment, it is the intent to
analyze a manned and unmanned aerial platform that utilize an automatic takeoff
and landing capability. The unmanned aerial vehicle of choice is the Solar HALE
UAV Electric High Altitude Solar Powered Aircraft (ELHASPA), which has both
automatic takeoff and landing. The manned aircraft of choice is the Northrop
Grumman F/A-18, with the AN/SPN-46 Aircraft Carrier Landing System (ACLS).
Manned Aircraft
Maritime Operating Environment and Safety Considerations
It should be noted that operating
environment and landing platform complexities may prevent or limit completely
autonomous takeoff and landing capabilities. Some platforms have automated
functions that are intended to supplement the pilot ability and act as a
secondary measure for assisted landings. For example, the Northrop Grumman F/A-18
Super Hornet has an automatic landing system, but no automatic takeoff system (Naval
Air Warfare Center Aircraft Division, 1998). The objective of the ACLS is to
ensure the safest possible approach, glideslope and landing to a pitching and
rolling aircraft deck (Naval Air Warfare Center Aircraft Division, 1998).
Similar
maritime platforms. While not a completely automatic takeoff and/or
landing, manned platforms such as the Sikorsky H-60 are equipped with an
automatic-departure and auto-hover feature, which allows the airframe to safely
arrive to and depart from a coupled hover with the help of the Automatic Flight
Control System (AFCS) (NAVAIR, 2014). The system limitations and standard
procedures however do not allow for departure with the weight-on-wheels switch
engaged (i.e. does not allow takeoff from a flight deck). Additionally, the
system has not been tested with the auto-approach function to landing since the
AFCS functionality relies heavily on radar altimeter (RADALT) feedback, and
this can present significant hazards on final approach course to landing (NAVAIR,
2014).
Based on some examples from manned
platforms, it is difficult to identify a manned aircraft that uses both
automated functions for both takeoff and landing routinely. Whether this is due
to overall system risk acceptance or the lengthy testing required to validate
system requirements and safety, it is surely a great tool to have in cases
where the pilot is unable to land the aircraft (due to fatigue or other
situations which would preclude the pilot from safely landing under manual
control). The Naval services may not advocate the automatic functionality for
routine use (outside of degraded ceiling and visibility limitations) due to the
overall risk associated with the system use (United Stated General Accounting
Office, 1986). The ever-changing conditions of sea-based landing platforms,
complex weather conditions, and the current success rates for automatic
landings based on complications with other aircraft subsystems and ship
conditions may limit the system use to only situations in which it is required (United
Stated General Accounting Office, 1986). Understanding the importance and risk
inherent in the ACLS and other automated systems can help shape the safeguards
put in place to prevent against mishaps.
ACLS
Required Training. The manned
operators of the ACLS are subject to NATOPS prescribed procedural compliance,
as well as standard operating procedures for the intended aircraft carrier, and
individual squadrons. The training for these systems is delineated in those
publications, including the periods for initial qualification to use the
system, and clearly identifies the training requirements and periodicity for
currency and proficiency. In addition to the requirements for the operator in
and out of the aircraft, there are currency requirements for the landing
signals officer (LSO) so that they can effectively monitor glideslope and
recognize ground station abnormalities and relay to the pilot (Naval Air
Warfare Center Aircraft Division, 1998). Initial and refresher ground training,
simulator training, and LSO training are all intended to promote safe and
effective system use.
Unmanned Operating
Environment and Safety Considerations
In terms of the Solar HALE UAV, which may be
used for a variety of missions, can be operated in a densely populated area,
among both unmanned and manned aircraft in congested airspace. The safety
precautions required to carefully evaluate the landing and takeoff capabilities
is important in meeting prescribed obstacle clearance on takeoff requirements,
runway length restrictions, and maintain clearances with other aircraft,
personnel, and structures (Laiacker et al., 2013). As there is no pilot onboard
the aircraft to account for variations in winds, changing runway conditions,
and adjusting glideslope/descent rate to execute a safe landing, the
characteristics of the automated system must be heavily scrutinized. Not
adhering to the guidelines established for local airports and controlling
agencies may make it even more difficult for UAS to attain acceptance and
establish routine operations within the NAS (Laiacker, Kondak, Schwarzbach,
& Muskardin, 2013).
Training Requirements.
For the unmanned ELHASPA, operators are trained to monitor the system
debugging, software, execute hardware in-the-loop simulations, and execution of
flight experimentation (Laiacker et al., 2013). Also, a designated safety pilot
is trained for steering the aircraft, and other pilots are trained to look out
for gaps in situational awareness and designing/changing system parameters based
on appropriate in-flight feedback (Laiacker et al., 2013).
Automated System
Capabilities and Limitations (Caps/Lims)
ALCS Caps/Lims. There are two
modes of operation for this system, Mode I is a fully automatic landing mode,
where Mode II is the manually controlled approach. If Mode II is selected
initially or if deselected after Mode I has been engaged, the cockpit display
will still continue to show ACLS information relating to lineup, glideslope and
throttle (Naval Air Warfare Center Aircraft Division, 1998). In the event of a
system failure that cannot be reset, the “COUPLER UNAVAILABLE” light will
illuminate, and discontinue use or not allow the use of the ACLS (Ellis, 2003).
Figure 1 below illustrates the ACLS entry window and a typical jet pattern
aboard an aircraft carrier prior to shipboard landing. Errors may occur while
in the ACLS pattern where rapid deviations in vertical or horizontal
displacement may produce a recoverable system error; in such a case Mode I will
be degraded and potentially alert for a switch to Mode II operations (Ellis,
2003). A clear limitation of this system is that it is intended for recovery
operations only.
It is possible that this system may be used
for the first time outside of the simulator in a real-time environment where
the ceiling and visibility ranges are not conducive for normal operations at
sea. If Mode I is unavailable, or unable to provide accurate flight corrections
due to repeated deviations affecting the sensitive system inputs, then it could
lead to a situation where a pilot is “not ready” or prepared for Mode II
operations. Eliminating the need for automation dependency by preparing pilots
with a rigorous air work curriculum and established policies delineating use of
the system should aid in this potential hazard. A similar situation may develop
where a pilot has never used the system before and has to use it to get back on
deck, in which case regular training and proficiency with the system will be
beneficial (Ellis, 2003).
Figure
1.
ACLS Pattern. Retrieved from AN/SPN-46(V)1 Automatic Carrier
Landing System (ACLS) Console Operating Procedures, Naval Air Warfare Center,
St Inigoes, Maryland, 31 March 1998
ELHASPA Caps/Lims. Inherently
there is a system limitation in the maintenance of electrical state of charge,
and attaining positive power margins (i.e. accounting for losses due to
relative impedance and solar cell efficiency) from the solar cells to the
electric motors (Laiacker, Kondak, Schwarzbach, & Muskardin, 2013). Ensuring
cell performance meets or exceeds mission life and power requirements at
altitude is surely a design limitation on the unmanned system itself. Inability
to maintain steady discharge rates in optimal ranges will severely impact UAV
flight characteristics in terms of throttle and power available to the engines
for takeoff or landing (Laiacker, Kondak, Schwarzbach, & Muskardin, 2013).
If there is inadequate power generated, then the flight path and automatic
takeoff and landing abilities could be degraded as a result. Figure 2 below
illustrates the system components for the automatic landing system, where
emphasis should be placed on the UAV using visual inputs to determine the
runway layout, location, and orientation.
The system accounts for course, speed, and
altitude to make direct flight control surface manipulations to allow for safe
landing. While the system may be able to account for these variables, the speed
and reliability in which the flight control computer is able to account for
rapid changes in external conditions (i.e. gusty winds and foreign object
debris) and effect a flight control change to correct may not be as reliable.
Future testing efforts to account for these external influences while
maintaining a small electronics package (to save on weight and cost) will be
beneficial for other solar powered UAS and small UAS. Additionally, the visual
inputs gathered to deduce runway orientation may be adversely affected by
deteriorating weather conditions that would otherwise hinder a visual system (Laiacker,
Kondak, Schwarzbach, & Muskardin, 2013).
For
this UAV, there is a manual control option as part of the control sources and
mode switch logic “decision tree.” Additionally, there is redundancy in
controlling authority for two pilots in the event of lost automatic functionality
or link, and is accomplished by using two safety pilots (Laiacker et al., 2013).
The main safety pilot manipulates the UAV using an RC-Transmitter relayed over
two long range radio modems, and the backup pilot uses the same transmitter
type directly from ground to the UAV; the handoff in control occurs when the
primary RC transmission connection fails (Laiacker et al., 2013). The main
limitation with this automatic landing system setup is that it is line of sight
(LOS) dependent.
Impact to safe operations and
safeguards. Aside from the option
of ejection in the manned F/A-18 platform, some safeguards could include: troubleshooting
after disengaging the system due to errors, anticipating the deviations in
drift due to ship movement, change in ship speed, or external weather
conditions (i.e. adjusting true aircraft heading to account for wind drift).
Regularly scheduled training and currency fulfillment, and continued
routinization of certification standards is a proactive method to solving potential
errors in the system (Ellis, 2003).
For the unmanned
element, redundant airborne and ground segments are available to the operators.
“In the event of a single failure the mission should be aborted so that a safe
landing can be performed” (Laiacker et
al., 2013). The rationale of only using double
redundancy is due to UAV weight and cost constraints. It is mentioned that many
UAS have a triple redundant system, so potentially incorporating that same
logic for the automatic control system as the UAS becomes larger in scale may
prove beneficial (Laiacker et al., 2013).
Figure 3 below illustrates the current redundant ELHASPA airborne segment setup
for takeoff and landing; it should be noted that there is a similar diagram
avaialble for the ground control segment.
Recommendations for automation. Simply
put, each platform conducting different missions should be evaluated to
determine which level of automation best meets the landing environment, user,
and owner of the system. For air operations at sea, it would be recommended to
exercise manual approaches to landing to the maximum extent practical, where
aircraft commander judgment should be placed in situations of extreme weather,
instrument meteorological conditions (IMC) and nighttime conditions. In the
case of the unmanned Solar UAV, it would be recommended to have both safety
pilots continue to monitor UAV inputs and assist as required to the maximum
extent possible for routine flight landing execution. Continued certification
testing under new and challenging conditions will allow for a more reliable
takeoff and landing system for unmanned aerial vehicles, and build confidence
for manned aircraft users utilizing recovery systems such as the ACLS.
References
Ellis, J. D.
(2003, August). A
Review and Analysis of Precision Approach and Landing System (PALS)
Certification Procedures. Retrieved from
http://trace.tennessee.edu/cgi/viewcontent.cgi?article=3297&context=utk_gradthes
Laiacker, M., Klockner, A., Kondak, K., Schwarzbach, M., Looye, G., Sommer, D., & Kossyk, I. (2013, June 19). Modular scalable system for operation and testing of UAVs. 2013 American Control Conference, 1460-1465. doi: 10.1109/ACC.2013.6580042
Laiacker, M., Kondak, K., Schwarzbach, M., Muskardin,
T. (2013, November 7). Vision aided automatic landing system for fixed wing UAV. IEEE/RSJ
International Conference on Intelligent Robots and Systems (IROS), Tokyo, Japan.
NAVAIR. (2014). Sikorsky MH-60R Naval Aviation Training Operation and Procedures and Standardization Manual, A1-H60-NFM-000. Norfolk, VA. United States Navy Air Education and Training.
Naval Air Warfare Center Aircraft Division (1998, March 31).
AN/SPN-46(V)1 Automatic Carrier Landing
System (ACLS) Console Operating Procedures. NAWCAD 4.5.8.1-140.
Riseborough, P.
(2004, July). Automatic take-off and landing control for small UAVs. 2004 Asian Annual Control Conference, 5(1),
754-762.
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