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Two Tcas Questions  
User currently offlineKaitak From Ireland, joined Aug 1999, 13264 posts, RR: 34
Posted (16 years 6 months 3 weeks 6 days 8 hours ago) and read 3117 times:

I was very surprised to hear (and please confirm?) that freight aircraft are not affected by the FAA directive on TCAS installation. I'm surprised because one would think that a collision involving, for example, a UPS 747 would do a lot more damage than one involving a small passenger commuter plane, like a Saab 340. Is this correct and why were freight aircraft not included?

(I'm assuming that aircraft delivered new to UPS and Fed Ex, such as the 767s and A300s, as well as the reworked MD10s, would have TCAS installed anyway?)

A question for pilots: is there any circumstance where a technical problem could cause the TCAS to become u/s? If so, what would happen in that case? Would the flight have to divert? Presumably the FAA would take a severe view if an aircraft was dispatched with the TCAS inop?

6 replies: All unread, jump to last
User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 27
Reply 1, posted (16 years 6 months 3 weeks 6 days 6 hours ago) and read 3080 times:

A TCAS alert resolution advisors told the pilot of a747 to climb in order to avoid another 747. It turns out the advisors told the pilot to climb the aircraft right into the path of the 747 it believed was below. The planes came within 200 feet of vertical seperation before the controller told the plane to begin an immediate descent avoiding the collision. I believe this happened about two weeks ago. I will look for the article.

I believe the TCAS to be a no go item. A flight would never made without it. If an in flight failure were to occur the plane could continue on to it's normal destination. The TCAS is not a primary collision avaoidance system. It is simply a back up to the controllers responsibility of aircraft seperation.

User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 2, posted (16 years 6 months 3 weeks 6 days 4 hours ago) and read 3069 times:

TCAS is only required in the USA. Several things can prevent it from functionning correctly from a faulty ADC to cross-talk failures between two or more Mode S units. TCAS is not required on all-freight aircraft or on passenger aircraft of less than 30 (I think that's the cut) seats.

TCAS will issue TA's (traffic advisories) only if both aircraft are NOT equipped with Mode S XPDR's. TCAS will issue RA's (resolution advisories) only if both aircraft are equipped with Mode S XPDR's. TCAS will tell you only that another aircraft is in the vicinity if the other aircraft has no TCAS, but is XPDR equipped.

TCAS still gets screwed up when more than two aircraft are involved in an occurence. TCAS also gets screwed up when one aircraft is climbing and the other aircraft is level. TCAS can also generate ghost targets.

RVSM on the north Atlantic came into being with the idea that TCAS would aid with loss of separation occurences. However, TCAS is not even required for RVSM ops. RVSM is now being introduced to the Pacific.

As stated, TCAS is only an aid to the pilot. Unfortunately it is still in its infancy, as seem to be some of the regulators who brought this program into being in the first place. If all a/c had TCAS, just like all aircraft have airspeed indicators, and the TCAS bugs were ironed out, it would be a fantastic addition to flight safety. Because like you say, whether you run into a C-152 or a (generic) 747 freighter, it will still ruin your day.

Best Regards,


User currently offlineJim From United States of America, joined Jul 1999, 455 posts, RR: 1
Reply 3, posted (16 years 6 months 3 weeks 5 days 23 hours ago) and read 3064 times:

We just covered TCAS in the 767-400 class I'm attending at Boeing. Here's how its supposed to work:

Basically, even if the other aircraft isn't equipped with the mode S transponder, it must have an ATCRBS (Air Traffic Control Radio Beacon System) transponder on board to fly in the airways system. TCAS can track up to 30 aircraft, which it divides into 4 categorys: OTHER-more than 40 seconds away and +/- 2700' altitude separation; PROXIMATE- more than 40 seconds away and +/- 1200'; INTRUDER- between 25 & 40 seconds away and +/- 1200', which generates a traffic advisory; and THREAT-less than 25 seconds away and +/- 900', which generates a resolution advisory.

If the confilicting aircraft isn't TCAS equipped, it will only be able to respond to interrogation by the TCAS-equipped aircraft with altitude data. The TCAS will command its own pilot to steer clear if necessary.

If the conflicting aircraft does have TCAS, than they both will 'talk' with data about aircraft type, speed and alitiude. The TCAS which first recognizes that there is possible problem will give the instructions for both aircraft to follow.

In short, not every aircraft needs TCAS, just the majority, to make the system work, as long as every aircraft flying in controlled airspace has at least an altitude-reporting transponder.........IN THEORY!


User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 4, posted (16 years 6 months 3 weeks 5 days 21 hours ago) and read 3062 times:

Jim: Are you going to be working with TCAS II or III?

Best Regards,


User currently offlineJim From United States of America, joined Jul 1999, 455 posts, RR: 1
Reply 5, posted (16 years 6 months 3 weeks 4 days 21 hours ago) and read 3059 times:


The 764 will be CATIIIc right from the box.


User currently offlineDash8tech From United States of America, joined Jul 1999, 732 posts, RR: 5
Reply 6, posted (16 years 6 months 3 weeks 4 days 19 hours ago) and read 3056 times:

Not a pilot, but I can tell you that TCAS can be deferred by the Minimum Equipment Listing for an aircraft, therefore they can be dispatched with TCAS inop-usually collaring the circuit breaker.


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