Obstacles To Low Flying Aircraft

aser · April 19, 2004

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OBSTACLES TO LOW FLYING AIRCRAFT

by Per Gram

Controlled Flight Into Terrain, CFIT; is a well known and to some extent a fairly well understood phenomenon. It usually follows breakdown of cockpit procedures or dicipline during IMC. When low flying aircraft hit power lines, the story may be somewhat more complicated.

It seems as if the number of such incidents and accidents are staying very much the same now as for 20 years ago. New systems which may make low flying safer are expensive and have not had time to prove their worth. However, just to make sure you hear my opinion on this, I have written this article.

HAI reports (Rotor & Wing October 2002) that there have been 66 wire strikes involving civil helicopters since 1996. An infamous accident occured in Italy a couple of years ago when a US Navy E-6 ?Prowler? on sightseeing cut a ski lift wire killing 20 people.

I have worked on flight safety for many years and I have flown a large mumber of aircraft and helicopters. Now and then it comes back to me that low flying in mountainous terrain may be the most challenging of all operations I know of. Low flying is defined as flying below 500` AGL outside of populated areas when you`re not established on an approved instrument procedure. Aerial work is usually low flying, large parts of HEMS operations and SAR may be low flying, law enforcement operations are usually low flying etc. Some of these operations may take place in mountainous or fjord areas like in Norway or a lot of other countries. These are all legal reasons for low flying. Power- and telephone lines are a constant threat to low flying in daylight but particularly during night. So, what do we have to help us?

You may first of all join a course wherby you get to understand the threat better. In fact, HAI`annual course, next time at Heli-Expo 2004 in Las Vegas, the theme is wire strikes. This is on March 14th. Read more about this on http://www.heliexpo.com/2004Fwand%20OEC.htm Or, you may buy a video on the subject from Transport Canada or from New Zealand CAA.

Maps.

Updated maps are crucial. For about 10 years we have had 1:250 000 digital maps for helicopter- and aeroplane operations in Norway. All man-made objects above 50` AGL outside populated areas, and above 100` inside populated areas are put on the map. All power lines accross fjords and valleys are depicted together with elevation of the towers at both ends. These maps are NOTAM`ed as well, i.e.

HELICOPTER-/LIGHT AIRCRAFT CHART (HLC) NORWAY 1:250 000 ? SHEET 10 AARDAL ? PUBLISHED 1992, AMEND:

POWERLINE TO READ POWERSPAN, ZIGZAG SYMBOL, 614756N0093451E, 2336FT AMSL ? 614809N0093412E, 1545FT AMSL

If this map is loaded into your aircraft`s computer and displayed on a moving map display, you will have a marvellous tool in your mental plot, situational awareness and particularly in your obstacle awareness. If your moving map display allows for vector graphics, you may actually peel off unwanted information. The definition of a moving map display:

(DOD, NATO) A display in which a symbol, representing the vehicle, remains stationary while the map or chart image moves beneath the symbol so that the display simulates the horizontal movement of the vehicle in which it is installed. Occasionally the design of the display is such that the map or chart image remains stationary while the symbol moves across a screen.

In the chart series mentioned above, there are lots of information you don`t need and it is just obscuring the information on power lines and terrain features you may be looking for. In other words, your moving map display needs a feature called map data extraction. Read about one knee pad type with all the recommended features on http://www.german-helicopter.com/Pages/con...arket_dkg3.html I am not advocating this particular system, it is just one of many products, but the declutter feature is ranked by far as the #1 feature amongst US Navy and Marine Corps tactical- and helicopter pilots ( Michael E. Trenchard, Maura C. Lohrenz, Stephanie S. Edwards, Naval Research Laboratory).

Millimetre Wave Radar

Some years ago I saw the Oasys (Obstacle Awareness System) radar at Farnborough. The demonstration there seemed impressive and the market for Amphitech`s system is growing, and last seen on Burt Rutan`s spectacular Proteus aircraft where it right now performs Unmanned Aerial Vehicle threat tests. The system will, if things goes right, be installed in the UAV`s so they automatically may perform evasive action when encountering other aircraft. Read more about its technical features on http://www.amphitech.com/english/s2/index.html This radar may also serve as a weather radar.

LASER

Another product is the German LADAR, earlier called HELLAS. This system will be installed in more than 100 German Army Eurocopter helicopters and in some NH90`s in other European countries. Check http://translate.google.com/transla...aser_radar.html for more information. Both the MMW radar and the LASER solution are

expensive systems, both manufacturers quote US$ 220.000 for a single installation (AW&ST October 9th 2000, and AIN March 2000). Just when this is being written, both systems are type certificated.

Terrain Awareness Warning Systems, TAWS

These systems are based on a database where certain geographical areas of the world are contained and presented on an EFIS, together with features you may be in particular need of. Jeppesen and others have a world wide database, which is also utilised by Honeywell, Universal Goodrich and Sandel in their TAWS or Enhanced Ground Proximity Warning Systems, EGPWS. Honeywell says that their helicopter modell EGPWS Mk XXII sells for US$50.000. This database contains about four times more data than similar for aeroplanes. Look up http://www.egpws.com/helo/helo.htm

Wirestrike Protection systems, WSPS (This wire cutter did its best?..http://hal9000.inetstrat.com/crash/oh58.html).t

The system is simply called wire cutter and is by far the simplest protection system available. It is fitted on top of and below the cockpit. It works if you hit the wire at a right angle. In the case above, the helicopter hit at least two wires. Wire cutters costs about US$ 6.000 and is certificated for several smaller types of helicopters.

ICAO

Recommendations on obstacle markings are found in ICAO Annex 14 Part I and II. In general, you`ll find that obstacle markings are only recommended in the vicinity of aerodromes and heliports. In Norway, regulations from 1998 also require markings on cables spanning fjords and valleys. The net of high tension wires in Norway has a length of about 80 000 kilometres. It is considered too costly and also too hazardous to mark older wires, so the moving map display, perhaps together with a MMW radar or EGPWS may make operations in my fjord country safer.

Regards

Aser