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• Safety issues
• Safety fears over pilotless planes
• Small UAVs should be treated as " birds" ...

Safety issues

• Any UAV with a take off weight of under 150 Kg must conform to national standards, such as CAA CAP 658 and CAP 722. Heavier UAVs need to conform ti international ICAO standards.
• Assume the UAV will, at some time, collide with a plane: the UAV must be made of readily destructible material, no harder than aluminium (in the engine) so that very little, if any, damage is done to the plane.
• The operating principle is “sense and avoid”:

• use sensors to detect fixed and moving obstacles in front of the UAV:

• 77 GHz automotive type collision avoidance mm wave RADAR
• scanning laser based LIDAR
• “distance aware” stereo imaging

• the collision detection computer must fuse data from the above sensors and issue instructions to the flight control computer, to avoid a collision.

• UAVs must be visible to both RADAR and the naked eye:

• use corner cubes at wing tips and an aviation Mode A or C Transponder
• use high power LEDs in the wing tips, to increase visibility at night

• Accident prevention features:

• emergency landing sites must be designated ab initio in the flight plan
• UAVs to fly in pairs, so one UAV can “nurse” a faulty UAV back to base,
• the UAV must support rain level detection, so it can return to base, if need be
• the UAV must be able to restart an engine in flight (eg. use compressed air)
• make use of in-built airbags, “armed” once the UAV is in the air
• aircraft operating parameters must always be monitored, to enable the identification of any impending failure
• a regular maintenance schedule must be strictly adhered to
• use multiple electrical power supplies and multiple communications links

• On failure of all communications links, for example, due to sunspot activity, the plane flies to nearest known base using GPS + IMU, or just IMU, based navigation

• If plane suffers from engine failure, or, major power blackout, then:

• dump fuel as necessary, to reduce weight and the risk of fire, on crashing
• deploy air brakes, to slow the descent of the UAV
• parachute or airbag(s) deployed, to bring the  plane slowly to soft landing
• activate Emergency Locator Transmitter radio beacon, to enable search planes with Radio Direction Finding equipment, to locate the downed UAV
• glide to a pre-defined emergency landing site

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• 10:52 27 June 2003
• Duncan Graham-Rowe
• http://www.newscientist.com/article.ns?id=dn3868

A plan for pilotless aircraft to begin operating routinely from ordinary airports in the US is being greeted with alarm by aviation safety campaigners. They say such operations would put at risk the safety of other planes, passengers on the ground and people living near the airports.

The plan, which also involves giving unmanned aerial vehicles (UAVs) easier access to US civil airspace, is the result of a powerful partnership led by the Pentagon, NASA, Lockheed-Martin, Northrop Grumman and Boeing. Called Access 5, the group aims to loosen restrictions on where UAVs can operate within 5 years.

For most of their flight, UAVs are controlled by a pilot on the ground via a satellite radio link. At present, anyone wanting to fly one in civilian airspace has to file a detailed flight plan with the Federal Aviation Administration (FAA) at least 30 days in advance.

Access 5 wants UAVs to be allowed to fly on the day the plan is filed, like any other aircraft. The group hopes that this rapid approval for UAV flights will allow the craft to fly more flexible missions. But critics fear it may eventually pave the way for pilotless cargo flights.

" Totally opposed"

The prospect of UAVs sharing runways with passenger planes is raising serious concerns. " What happens if a pilotless plane hits an airport terminal or another plane?" asks Gail Dunham of the National Air Disaster Alliance, an airline safety pressure group based in Washington DC. " We are totally opposed to this plan."

Warren Morningstar at the Aircraft Owners and Pilots Association in Frederick, Maryland, says avoiding collisions with other aircraft is the major concern. " How do you accomplish that when you don't have a pilot on board?" he asks.

UAVs have been used for military scouting and attack missions in Iraq, Afghanistan, Kosovo and elsewhere. But they will also become important to civilian scientists performing environmental monitoring, volcanic observation and atmospheric sampling because they can stay aloft far longer than piloted planes.

A group led by Glenn Hamilton of NASA's Dryden Flight Research Center in Edwards, California, has modified a military Predator UAV for such applications. Called the Altair, the craft made its maiden flight earlier in June.

Radio link

But before such a UAV is allowed to fly in civilian airspace, its operator has to prove to the FAA that it has an equivalent level of safety to a piloted aircraft. This is a lengthy process that currently takes between 30 and 60 days.

The operator files a detailed flight plan with the FAA, listing every detail of the craft's journey: where it will be flying, how it is controlled and, perhaps most importantly, what will happen if the radio link with the pilot on the ground is lost. Only then will the FAA allow it to take off. These restrictions mean that UAVs only fly in controlled US airspace about 10 times a year.

Advocates of UAVs say these controls are far stricter than they need to be. The Pentagon admits that the Global Hawk UAV has a crash rate more than 50 times that of F-16 piloted fighter jets, and has set a target to reduce this by 2009 (see graph). Even then, the 25 crashes per 100,000 flying hours that the Pentagon is aiming for will still exceed that of piloted planes.

But the UAV's proponents claim these figures can be misleading. For example, when a military UAV fails to return from a mission it can be impossible to tell whether it was shot down, or crashed because of a systems or communications failure.

Line-of-sight

One crucial question for safety campaigners is what will happen if the link between the ground pilot and the UAV is interrupted while the craft is taking off or landing.

Hamilton describes the chances of this happening as " minuscule" , because for these operations there are two direct line-of-sight radio links, rather than just a satellite link.

But airline safety analyst Todd Curtis of Airsafe.com insists that plans must always be in place to deal with the loss of the control link, however unlikely that is.

Denis Chagnon of the International Civil Aviation Organization in Montreal believes global civil UAV operations are, ultimately, unstoppable. " Pilotless aircraft are coming," he says. " We just have to be ready for them."

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An interesting suggestion that small UAVs should be treated as birds was made by Olle Hagner in his presentation on " Inherently safe UAS by design ..." at the UAV 2007 Conference in Paris. The bird statistics are for Sweden.

However, as pointed out by Cliff Whittaker of the U.K. CAA in his presentation of " UK-CAA policy for light UAS systems" at the UAV 2007 Conference in Paris  by D Haddon and C Whittaker, the larger birds can inflict some severe damage on aircraft (with the aircraft inflicting even more damage to the bird). Below, a copy from the same presentation.

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