Technical

Traffic avoidance for Helicopters

And how FLARM can help

Helipaddy fly an R44 in the southern UK which has a very active gliding and GA community. They have installed a FLARM device for peace of mind.

  • Appendix 1: ADS-B and what the heck is it?
  • Appendix 2: How do I install FLARM?
  • Appendix 3: Airprox reports in GA
  • Appendix 4: VFR/IFR rules for gliders

Copyright Helipaddy 2017. Do not re-use any part without permission.


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Traffic avoidance in general

Unfortunately, in our experience some airfields increase risk with the use of same height VRP’s for all traffic, unnecessarily complicated instructions or “scary” controllers. Traffic detection devices are going to be of limited help near the circuit and radio operators can only provide limited context. A good understanding of the circuit heights and procedures helps to create a picture in our heads of where the movements are likely to be. Avoiding “standard” heights at busy reporting points is something we try to do.

During flight, nothing beats looking out of the window and using the “scanning” system effectively, but that is far from foolproof and so traffic awareness systems do provide a 2nd pair of eyes.

We have flown small fixed-wing aircraft in various configurations and amazed at the lack of visibility in the front seats. Helicopters and other aircraft cannot easily be seen at the same height. LARS can help but traffic services are not usually provided below 1500 ft.

Some regulatory-minded people are proposing flight plans for all flights. We would be strongly opposed to such a retrograde approach, having recently done some pretty miserable flying in Egypt recently. A whole new set of unintended dangers arise.

Gliders and glider pilots

Helipaddy flew in to Lasham to visit Shaun from Lasham Gliding in the UK, the worlds largest gliding site by membership. Over 220 gliders are based at the airfield which is in constant use throughout the year and regularly hosts national and regional gliding championships.

What gliders look like when you can actually see them

We started out by learning how to best avoid gliders when we are flying around the UK. The incidence of glider/helicopter collisions is extremely low (we couldn’t find any actually) however the anxiety factor is heightened when near gliding sites and we wanted to find out more.

Glider pilots love clouds. VFR heli pilots hate clouds. In fact, gliders have a dispensation to fly into clouds and they even have a “cloud” frequency of 130.400MHz*. Clouds mark the tops of thermals and indicate where moist air has risen to the point where the colder temperature condenses it. This means that plenty of gliding activity could be expected at or near the cloud base. Higher clouds, say 3000 feet plus, may indicate stronger thermals and better gliding days. High winds aren’t particularly pleasant for any aircraft and will reduce gliding activity, as will no wind at all. A good gliding day is known as a “soarable”day.

Gliders play around in the orange area

They also like height and a bit of speed. A typical modern glider might have a slope of 60:1 and a cruise speed of 100 knots, with a stall speed of 50 and a VNE of 150. At 3000 feet, in no wind, they will travel 30nm for 20 minutes before landing. Whilst playing around at cloud base, or along a street of clouds, they will be doing a similar speed to the R44. Shaun explained that a typical glider is always descending at about 1.5 knots (150 ft/min). After 20 minutes, it will descend 0.5nm or 3000 feet.

It is somewhat counterintuitive that glider pilots often ballast their aircraft with water. On a high lifting day, where the lift is significantly more than 1.5 knots, the aircraft would be too light, or it would need to be an attitude that would make it too fast. The ballast allows for a comfortable attitude and airspeed with higher kinetic energy. Kinetic energy is useful for pulling up and gliders will climb several hundred feet in a few seconds.

140kt of airspeed near the ground can translate into 50kt some 500’ higher up in as little as 5 seconds so be very careful not to get above gliders that are travelling back to an airfield at what seems to be a low altitude but at high speed. Here is text to check copyright. When a competition is under way (usually NOTAMed well in advance) this sort of high speed arrival and pull up is very likely, the competition pilot wishing to cross the finish line at maximum speed before using the excess energy to gain enough height for a short circuit. The ballast is jettisoned before going back to land.

Most gliding is A to A, rather than A to Z, as students have to practice a lot of landings (1.5x your age as a minimum). But cross-country events are popular so gliders will be anywhere in the UK, not just near gliding sites. The UK distance record is over 1000 km in one flight! If you happen to spot one glider climbing, there is a good chance that others will come and join the thermals and there will therefore be a spiral of them. They tend to do about 20 second full circles. Keep well clear!

If you want to be aware of them you will need to use FLARM in the cockpit, as it is the only existing and widely used cooperative collision warning system for GA. FLARM is installed in almost all gliders in Europe.

FLARM: for situational awareness

PowerFLARM Core is the new updated FLARM/ADS-B traffic awareness and collision avoidance system and can detect:

  • FLARM-transmitting traffic (most gliders, and many GA airplanes and helicopters)
  • ADS-B (some aircraft) — see the Appendix for a description of ADS-B
  • Most transponders (almost all aircraft)
  • Many obstacles in the FLARM database

There are many FLARM devices available on the market from different manufacturers. The three FLARM devices designed especially for helicopters and other GA aircraft are shown below.

PowerFLARM Portable / TRX-1500 / PowerFLARM Core

The Portable and Core are similar products but the Portable clearly avoids some installation hassles and you can connect secondary displays (like SkyDemon or Garmin) to the Portable as well. The biggest difference is that Portable uses internal antennas, mounted directly to the back of the device. Core normally uses external antennas, mounted on top and bottom of the aircraft (just like transponder antennas), although in a helicopter, with all the glass, it is fine to use internal antennas. The TRX-1500 is slightly cheaper than the Core but is based on the old, legacy Classic FLARM technology. PowerFLARM Core and Portable are based on the new PowerFLARM technology. This implies much longer range, radio (antenna) diversity, better interference protection, and EASA installation approval. See Appendix 2 — Installing FLARM.

When checking prices, make sure you are comparing the same -feature models. The Core is around £1400 (plus £400 for the primary “AIR Traffic” display), the TRX around £1200 and the PowerFLARM Portable unit around £2100. PowerFLARM Core is considered a Minor Change by EASA and can be fitted into a G-reg R44.

FLARM isn’t seen as a competitor to ADS-B as ADS-B is for long range ATC separation, while FLARM is for short range collision avoidance. FLARM uses the lower-accuracy position from ADS-B Out aircraft that do not yet have FLARM. In addition, it’s important to note that FLARM doesn’t just send the GPS position, but the 3D flight path trajectory for the next 20 seconds. This is a huge difference to ADS-B. All FLARM devices are both receiving and transmitting, whereas a Transponder which is transmitting GPS position is by definition ADS-B (also called 1090 ES = Extended Squitter). It’s also not for air-air use, but for air-ground use by ATC. The only other air-air technology is TCAS, which uses transponder signals as well.

A PowerFLARM Core ADS-B device is ideal for any pilot who wants to see and get collision warnings about all traffic, and also be seen by all the other FLARM equipped aircraft.

We installed a Portable unit in our R44 and connected it to Skydemon. The one disadvantage is that your iPad must connect via Wifi (using the Air Connect). Helipaddy will also soon be displaying a traffic overlay which will be handy when a formation are flying in to a private site. The Air Connect unit is around £160.

What we see now in our R44

The glider market is no longer the primary one for FLARM these days. Historically (more than a decade ago), it was developed for gliders and most installations were in gliders, mainly because of the low power consumption, small size and importance of situational awareness.

Today, however, most installations are in GA airplanes and helicopters. 35,000 manned aircraft already have FLARM, which is around half the European fleet. With the current installation rate, almost all GA aircraft in Europe will have FLARM installed within 10 years.

REGA and ADAC, the rescue helicopters in Switzerland and Germany, respectively, have FLARM in all their helicopters. In Germany, the police and border patrol helicopters all have FLARM. It’s also taking off as the primary means of collision avoidance and remote identification in drones.

Going in to gliding sites

When flying into or near a gliding site, it is helpful to know what sort of activity is going on. On a nice soarable day, there will be 200 launches of which around 2/3 will be via the winch and 1/3 via a tug. 130.100 is a good choices and you should encounter banter almost anywhere in class G.

The winch can go up to 3500 feet whilst the tugs will typically go to 2000 feet. The tugs are easy to see but the winch cable is invisible other than the parachute which is attached to the hook end. The winch will be at the downwind (far) end of the runway so it is a simple rule to keep completely clear of the downwind end of all runways, and some gliding sites will have 3 runways. That means no deadside or overhead joins either.

The glider circuit is very tight compared to powered circuits, and they also cut the corner at 45 degrees when turning onto base leg. Typically an arriving glider pilot positions to be upwind of the airfield when at 1000ft agl and aims to start the gliding circuit (in the area at the start of the downwind leg) at a point known as “High Key” (approximately 800ft agl). The pilot will usually make a downwind call but there will be no base or final call as the gliders do not have “Press To Transmit” fitted to the control column and the spare hand is required to operate the air-brake in the latter half of the circuit.

The glider will be abeam the touchdown reference point know as “Low Key” (500–600 ft agl) and will continue downwind before turning 45 degrees onto a diagonal leg so as to keep the landing area in view. Depending on wind strength and glider type the glider will make a further 45 degree turn onto base leg followed by a final turn (completed by 300ft agl). Sometimes a glider on a winch launch may only achieve 800ft agl, so will be straight into the circuit.

High performance gliders returning from cross-country flights may be making straight in approaches at speeds up to VNE (150kts) before pulling up and joining the glider circuit. They may also be dumping water ballast at the time which will look like smoke.

For those pilots that do find themselves routing South west from London, Lasham Gliding request that you route overhead Popham. Do NOT overfly gliding sites and keep well clear of the 800ft AGL level on the downwind side. If going in to land, use the radio and go in very low and slow and stay on frequency.

If you want to where the gliders are now, click the image below.

130.400 MHz
Cloud flying and relaying cross-country location messages only.

130.125 MHz
Primary Use: Training (lead and follow) and cross-country location messages.
Secondary Use: Local flying; competition start and finish lines.

130.100 MHz
Primary Use: Competition start and finish lines; local flying.
Secondary Use: Training (lead and follow).

129.975 MHz
To be used only as a gliding airfield local control frequency within 10 nm radius and below 3000 ft. May be used by power aircraft requiring clearance through a gliding airfield circuit.

129.900 MHz
Ground to ground and retrieve recovery only.

Click image to view some gliding sites in the UK and which ones you can fly in to. At the time of writing, the CAA point out that Wethersfield, Upottery, Aston Down, Saltby, Metfield, Burn and Driffield are active and not abandoned as shown on the 2016 charts.

Appendix 1: ADS-B and what the heck is it?

ADS-B stands for Automatic Dependant Surveillance Broadcast. When you are equipped with ADS-B Out, your GPS position and other information will be transmitted to ATC ground stations. This information can also be received by ADS-B In-enabled aircraft, like PowerFLARM Core ADS-B. The ground stations share the data which is why you can sometimes see yourself on FlightRadar etc.

ADS-B Out is becoming compulsory in the US (but not in Europe) whereas ADS-B In is optional. ADS-B Out data is transmitted by the Transponder (the transmitting without being interrogated is called “squitting”). It broadcasts the position, ICAO 24-bit address, and other information. Normally, ground stations hold a registration database so that they can then share the aircraft data as well.

ADS-B out equipment (both the certified GPS and transponder/ squitter) must be panel mounted and cannot be portable. However, FLARM, since it is not required by regulations, can be portable.

In general, EASA usually considers the classification of any change that introduces ADS-B to be a major change — ie a Major Mod costing thousands in approvals paperwork as compared to a FLARM installation which is a Minor Change only**. The problem with ADS-B is that it was developed for ATC purposes only, i.e. several nautical miles of separation. Most legacy certified GPS devices used for the position have very bad accuracy (the “certified” part is not related to accuracy, but to fault reporting, etc.). You don’t even actually need GPS as a position source. Older aircraft use IRS, etc. So if you try to use the ADS-B position from an aircraft for short-range collision avoidance, you might have several 100 m error, which is obviously not ok.

Second, the important part of a collision avoidance system is giving timely — but not too early – and accurate collision warnings. Just showing aircraft on a screen can actually reduce safety (confusion, too much instrument time, false feeling of safety, etc.). So even if the position source of an ADS-B aircraft is accurate, an ADS-B In solution in itself won’t increase safety. PowerFLARM Core ADS-B however includes an ADS-B and Mode-C/S receiver, so these aircraft are included in the collision algorithms as well.

To help encourage ADS-B take-up by the GA community, the CAA has recently launched a survey seeking information on the types of devices private pilots already use (https://www.surveymonkey.co.uk/r/UKGAEC).

Appendix 2: How do I install FLARM?

There is a misconception that Garmin or SkyDemon are sufficient as the display which arises from the belief that only seeing proximate aircraft on a display will increase safety.

If you have only one aircraft approaching you from the side, you are both flying straight and level, and you happen to look at the screen at the right moment, you might be able to avoid. But even then it will be very difficult to discern if the flight paths will intersect. In other cases, normally during approach/departure, where many mid-airs happen, with many aircraft around you, lots of radio traffic, etc., it will be impossible to look at the display at the right moment and at the same time evaluate the collision risk. This is why it’s so important to have collision warnings, which is the core function of FLARM. To show aircraft on a moving map is a nice-to-have, but doesn’t normally increase safety. It can actually decrease safety if pilots look at the display too much, or get confused, etc.

There has however been a lot of research on this subject, and as with many other safety issues, general perception is often contrary to how it actually works. Hence both a display (built in to the Portable) is essential.

Core is normally mounted behind the panel whilst a primary display is installed in the panel. The Core and the display need to be powered via a separate circuit breaker. Antennas are installed (usually internally near the window) and connected to Core. A second ADS-B/SSR antenna is installed in similar fashion.

EASA has formally approved PowerFLARM to be installed in helicopters and is considered a “Minor Change Approval” (MCA)to the type certificate of the aircraft. The approval is formally called EASA Minor Change Approval, or MCA for short and works for most aircraft below 2 tonnes.

Installation of FLARM can also be carried out as a standard change; however, in that case limited to day VFR. It requires essentially the same documents as the MCA, but can be approved by the installer without involving EASA.

The MCA includes approval for installation of external antennas (including the new external FLARM antenna) as well as compatible FLARM displays.

Firmware updates are not only useful but actually mandatory every year. Make sure to use a micro SD card that is under 32GB and formatted as FAT, not exFAT (my GoPro card wouldn’t work).

Helipaddy are able to assist with the pricing and purchase of FLARM devices. Contact us at support@helipaddy.com or buy now from LX Avionics and earn a Premium Helipaddy subscription for free.

Appendix 3: Airprox reports in GA

Courtesy of airproxboard.org

There were 154 Airprox in 2015 in which at least one aircraft was GA (71% of the total 217). Although this is a welcome reduction since 2014 where there were 171 incidents, it still represents a markedly high absolute number of incidents compared to the last 10-year period. That being said, the percentage share of Airprox involving GA has historically remained fairly consistent at between 61% and 76% over the last 10 years; 2015 remains within this band. This reflects that GA represents the majority of flying activity in Class G see- and-avoid airspace, which is where most incidents occur. Of the 2015 incidents, the clear majority occur below 3000ft in Class G airspace as shown in Figure 32. However, of concern, the second most common airspace for Airprox is within Aerodrome Traffic Zones which should provide a highly structured and known environment, but still accounts for a significant number of events largely resulting from poor airmanship, poor situational awareness or lack of consideration for other airspace users.

Poor knowledge/appreciation of others (specifically, gliders, parachuting, microlights, hang-gliders etc) was evident in a number of incidents. In particular, the number of incidents where aircraft have flown through glider/microlight/parachuting sites indicates either poor GA awareness, or a lack of consideration for winch-launching, glider towing and other associated sport-aviation activities. On the other hand, gliders and microlights soaring or transiting across airfield approach lanes or in IFR holds indicates similar lack of knowledge and appreciation of GA procedures.

Appendix 4: VFR/IFR rules for gliders

According to CHIRP: When operating under VFR pilots — both Power AND Glider — must observe the appropriate rules for separation from cloud i.e. for flight above 3000ft: 1500m horizontally and 1000ft vertically clear of cloud. This is a true statement, if operating under VFR. However, it is also true that glider pilots can operate under IFR and fly closer to cloud than 1500m/1000ft, i.e. fly in IMC. Operating under IFR would normally require some kind of instrument rating for powered pilots but glider pilots are not required to hold a licence (this is expected to change under EASA regulation in April 2018) and consequently have no requirement to hold an instrument or cloud flying rating (the requirement for which is defined within the licence) in order to operate under IFR. The net effect is that currently in the UK in Class G airspace, a glider pilot can legally operate under, around (within 1500m/1000ft) and in cloud, whether below or above 3000ft amsl. In practice, practically all UK glider pilots operate under the auspices of the BGA or a military club with BGA affiliation, which ensures a robust framework of pilot certification and risk management, including training for activities such as cloud flying.


**According to PPLIR: However, a modification may be classified as a Minor Change if the following conditions are met:

  • Transponder is ETSO-2C112b approved and complies with the requirements of ED-102/DO-260 or DO-260A
  • GNSS receiver is approved under ETSO C-129A, TSO C-129, TSO C-129A, ETSO C-145/C-146 or TSO C-145A/C146A
  • Direct interface exists between transponder and GNSS receiver
  • Latency (less than 1.5 seconds/95%) issues are a major concern (ie not broadcasting a position that is already out-of-date).

Last part is courtesy of https://www.pplir.org/using-the-rating/1006-explaining-ads-b-and-tcas-feb-2014

** Risk categories
A. Risk of Collision: …aircraft proximity in which serious risk of collision has existed

B. Safety not assured: …aircraft proximity in which the safety of the aircraft may have been compromised.

C. No risk of collision: …aircraft proximity in which no risk of collision has existed.

D. Risk not determined: aircraft proximity in which insufficient information was available to determine the risk involved, or inconclusive or conflicting evidence precluded such determination.

E. Benign

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