TCAS

[muffin]

TCAS
Not sure if this is the correct forum to ask this question, but are Mil rotary aircraft fitted with TCAS?

My house seems to be right under a regular route for very low flying Chinooks which I think is great, except that I nearly met one yesterday at about 200 ft just as I was climbing out from my helipad. Would a big White H get recorded by them for future reference or is it just a case of Mk 1 eyeball?

I always squawk 7000 mode S but wonder if it has any effect.

[isaneng]

Some aircraft are TCAS equipped, some aren't - I'm sure a Whokka mate will confirm or deny as required. And if you're operating under a busy helo transit route, a quick call to Odiham flight planning might be an idea...

[TurbineTooHot]

It would be worth getting a dialogue going with Odiham Flt Ops. A bit of friendly coordination goes a long way.

I find it unlikely that the Wokkas have TCAS, so they'll appreciate knowing that your pad is active.

[heights good]

Muffin,

Is your HLS marked on aviation maps? If not then crews will have other things to be looking at rather than seeing if every piece of real estate has a huge white H on it. That is not said to sound flippant, I mean they actually genuinly do not have time too look for every eventuality that might happen on the ground.

It's difficult enough with horses, avoids, chicken farms, farm strips, heli avoids, LFA boundaries, etc. etc.

The best piece of advice I can give you is to speak to Odiham AND Benson, Middle Wallop, Yeovilton, Wattisham, Dishforth, Culdrose Ops. The easiest option is probably AIDU at Northolt to have you HLS marked on the latest maps. :)

I hope this helps.

HG

[KG86]

A better question might be "Why haven't ALL UK military ac been fitted with TCAS?"

Even the Grob Tutor is now TCAS equipped. I find it inexplicable that SH in particular, with potentially large numbers of pax, have not been fitted with this cheap, off-the-shelf flight safety enhancement. I would call it corporate negligence.

[Just This Once...]

Merlin MK3A...

[High_Expect]

TCAS isn't as good as you would have thought! In it's comfort zone ie. above 1000ft and below 300kts it's fine, however, stick it in a fast jet and it is at best unreliable and at worst inaccurate and distracting. I know this is a wokka related thread but everywhere I go now all I hear is TCAS would mitigate the risk and it's just not true. I believe there was a close call between a Tutor and a Hawk recently at low level and both have TCAS!

[Runaway Gun]

I believe there was a close call between a Tutor and a Hawk recently at low level and both have TCAS!

Until TCAS actually has control over the stick and throttle, there is always the potential for close calls. Both sets of crew need time to be alerted, and then to react sufficiently in time. If it was a close call, and not a collision, then maybe TCAS did it's job !!

[High_Expect]

Agreed, may it did prevent a mid air. But to all those that seem to believe TCAS will always warn of a potential collision I'm afraid your wrong. From what I've heard the Tutor saw/heard nothing and the Hawk was given a traffic call within a few thousand feet.

[MG]

No RAF SH cabs have it as far as I know. The Merlin Mk3a came with it but it was disabled as it wasn't supported, just like the radar ( and that of the Chinook Mk3). I do my best to be loyal, but sometimes you just have to cry with the short-sightedness of it all.

[high spirits]

God forbid some well known flying organisation might have bought say, six ac and then removed the TCAS because they couldn't afford to fund it. What would Hadden-Cave make of that?

[Trim Stab]

it is at best unreliable and at worst inaccurate and distracting.


I think that depends partly on how the information is interfaced to the pilot, and the processing power of the graphics interface. Some of the synthetic vision PFDs with TCAS integration available now on civvy bizjets present the exact position of potentially conflicting aircraft on the PFD panorama with remarkable precision and intuitiveness. There is no discernible lag or inaccuracy at all - if an aircraft appears on the PFD - look up and it is there exactly at the distance and azimuth you expect.

[PPRuNeUser0211]

The present tutor display is pretty decent. It's well integrated into the HSI, so is part of the normal scan and very good for keeping SA. The problem with the kit is that as commented above, when it works it's bloody brilliant. However, sometimes it just doesn't pick up something, and even worse sometimes it picks something up but puts them in the wrong place. This is, I'm led to believe, an issue with the several meters of spare cable for the antenna that they've carefully coiled up in the fuselage....

The best bit about it is the height readout for other aircraft, being just about the only bit that doesn't usually lie to you and gives you a very big comfort factor!

[ShortFatOne]

In the circumstances you describe it is unlikely that TCAS would have been much use anyway.

The following applies to most commercially available TCAS systems.

When a TCAS 'sees' another TCAS fitted platform indicating below 370ft agl (Mode 3C or Mode S), it does not display that low level contact because TCAS assumes that the platform is in the process of landing/taking off - one of the many filters applied to prevent saturation overload.

If you and the other platform are both between 370ft and 920ft, then you should both get Traffic Advisories but no Resolution Alerts (filter to prevent TCAS trying to point one of the aircraft at the ground.

Oddly enough, one way around the low-level issue is to just Squawk Mode 3A (no height feed). Because TCAS can detect the Mode 3A but no height feed it will display you as other traffic (on systems capable of displaying Other/Proximate Traffic). I am not advocating this behaviour in any way, it is just a function of the system and is for information only!

I agree with previous posters, contact both NATS and No1AIDU and highlight your concerns. TCAS is damned useful but not the necessarily always the answer.

[the funky munky]

There is no requirement for TCAS for Military Rotary Wing aircraft, confirmed by DE&S Safety gurus. TCAS works only if both parties have it fitted and also best at altitude. Apparently at the sort of altitudes helicopters operate there are lots of false alarms.

The Merlin 3A may have come with it fitted but again not a requirement and comes with a training and currency burden.

[ShortFatOne]

I wasn't clear enough in my post above. Only one platform needs to be TCAS fitted. So long as the other platform is at least Sqauwking Mode 3C then the TCAS fitted platform will still 'see' it a react accordingly (As long as it is above 370ft). It just won't be a co-ordinated event between 2 TCAS's.

As I also said, assuming that most Helo's operate below 370ft agl, there won't be any 'false alarms' because TCAS suppresses all TA/RAs when the operating platform is below 370ft (Other Traffic may be displayed in some cases, but only if they are Sqwauking Mode 3A, not C).

Finally, using the training/currency expense card is just an excuse. I know DE&S has a whole bunch of TCAS courseware/CBT that could easily be modified to a particular fit (all TCAS operate in a fairly similar way). How do I know, 'cos I wrote most of it, as well as delivered and taught it, in the classroom and the simulator (before the Government scrapped the aircraft). :sad:

[high spirits]

Funky,
Your use of the words 'DE&S' and 'Safety Gurus' convinced me that you don't know what you are talking about. Unless that was sarcasm in which case I apologise.

TCAS does work down below, very well. Are the regs changing to make it mandatory for some controlled airspace. National standby rotary might find themselves shut out of London for example.

[PPRuNeUser0211]

Sfo- the tutor TAS (As distinct from tcas ) will give you display & alerts from traffic at any height. Actually useful as you can 'see' aircraft on the ground at minor aerodromes/before they get airborne ....

[High_Expect]

What does TCAS use as it's terrain reference? With FJ obviously rad alt but what about AC not equipped with one?

[frodo_monkey]

AIUI no link to radalt, it uses your Mode C height (giving everyone a common datum -1013.2)...

[Just This Once...]

A bit of confusion here as (from my failing Sunday memory) TCAS uses a Sensitivity Level (SL) to determine the alarm time, the protected area and the vertical threshold for TAs and RAs - your protected virtual box.

For SL 2 and 3 radalt is used (0 ft agl to 1450 ft agl) and for SL 4 to 7 pressure altitude is used. When radalt and pressure altitude calculates different SLs, the TCAS uses the lower SL. Therefore, when a valid radalt is present the radalt signal is used to determine the SL. With no valid radalt signal, or no radalt fitted, then pressure altitude is used.

[High_Expect]

So given this magic 370ft figure depending on the QNH of the hour when flying at 250AGL radalt you may or may not get TA's? Doesn't sound right to me. I understand the logic of the RA's being generated on 1013.2 but if there is an operating mode step change at 370ft how does it know?

[isaneng]

I have used TCAS on 3 types, but all multi's, so therefore prob using the same logic. They have all used a radalt input below about 1000 ft to place it in TA only, and have inhibited some RAs below about 1500ft (ie: increase descent). But they have displayed all contacts even when at low level, (or even on the ground) with the contacts height using pressure alt as the datum. From some of the numbers discussed here, I can only presume different types use different logic software.

[Brain Potter]

There appears to be some confusion being generated by the misuse of the term "height" instead of altitude (a common trait amongst Brit Mil Aviators, probably due to their upbringing on QFE).

The TCAS uses the altitude encoding of Mode S or Mode C to calculate differential altitude of conflicting traffic with all systems referenced to Standard Pressure Setting. The altimeters of the conflicting aircraft may be set to different pressure settings, but the differential altitude information displayed to the pilots and used by the TCAS for calculating the RA is always based on the equivalent flight levels. The only height input required is that of the radio altimeter, in order to inhibit the RA mode when close to the ground.

I am not aware of how TCAS would work in aircraft without radio altimeter, but remember reading that the system fitted to the Tucano was effectively a TA only device, with no capability to generate RAs. Maybe that is because with no radio altimeter for height reference the system could not safely operate in an RA mode.

[High_Expect]

Does anyone know where we can get a service source of information on the operation of TCAS. Clearly AP3456 is woefully out of date and doesn't even cover TCAS.

My type has TCAS but the manufacturer won't give us information on it as it is made by a third party, and the third party won't give it to us as we are not the customer in their eyes. A stupid situation I know and one I'm starting to lose patience with. Effectively we are operating with it without knowing its limitations! Do you think I should give the MAA a call and see if their weight has any influence?

[Just This Once...]

Honeywell do a very comprehensive set of TCAS manuals that can probably be found on the internet. Your Topic 15A should detail the TCAS installation and limitations for your type (although I know not all do).

Some good cautions above regarding height vs altitude that are worth remembering as it is all SPS related for actual TAs/RAs. It also worth remembering that not all Brit Mil types have upper and lower directional TCAS antennas, usually relying on an omnidirectional antenna for the lower. This is allowed by civilian regulations but can deny the SA provided by the plan display if airframe or antenna blanking come to play. If the system is TA/RA capable you will still get a 'no bearing' alert but it can cause confusion and much angst! I personally feel that twin directional antennas are a must for military use where the SA provided by them in some operational airspace is pretty much vital.

TCAS is vital for all military aircraft, even if its use is not always appropriate. We all transit straight and level in close company to regular traffic from time to time. Not having TCAS fitted to our ac is just plain silly - the Boulevard at night or in poor weather can be rather shocking!

[ShyTorque]

Apparently some here are talking about TCAS 1 and others TCAS 2.

TCAS works only if both parties have it fitted and also best at altitude. Apparently at the sort of altitudes helicopters operate there are lots of false alarms.

I don't understand this post; both sentences in that statement are incorrect for TCAS 1.

I've flown four different models of TCAS 1 equipped helicopters for a living for over a decade (or TAS, depending on manufacturer). These are police and corporate aircraft (three different types in the latter role). TCAS1 will only give traffic advice/alert, not any kind of resolution. If one aircraft has TCAS 1 it only needs to receive info from a working transponder to pick up the other aircraft and display it on screen. In my experience, false alarms are seldom given, at any altitude, with this equipment.

However, a limitation (apart from non transponding aircraft....) is when transponding aircraft are "squawking" Mode A. The TCAS cannot take into account an altitude difference because it has no information and will therefore generate an "over-cautious" alarm (Traffic Advisory) based on horizontal separation alone (as per an ATC primary radar). This is not a false alarm per se, because there is an aircraft somewhere close by in azimuth.