# What is the rationale of a weight/passenger value for the ICAO TCAS requirement?

What is the rationale for the figures 5,700 Kg and 19 passengers?

Excerpt from TCAS's Wikipedia entry page:

It is a type of airborne collision avoidance system mandated by the International Civil Aviation Organization to be fitted to all aircraft with a maximum take-off mass (MTOM) of over 5,700 kg (12,600 lb) or authorized to carry more than 19 passengers.

• I would guess costs-benefits tradeoff – Federico May 24 '14 at 10:37
• Can you expand please? – menjaraz May 24 '14 at 10:52
• The specific numbers were probably chosen with a representative list of aircraft in mind. The lawmakers may have done a cost/benefit analysis on several planes, and decided which ones it made sense for. Then a number that included and excluded the appropriate planes was chosen. This is heavy speculation on my part though. – TypeIA May 24 '14 at 12:48

The numbers aren't random, though at first glance the rationale may not be obvious.

### Weight

5700 kilograms is (roughly) 12,500 pounds - This aligns with the FAA definition of a "large aircraft" (an aircraft with a maximum certificated takeoff weight of more than 12,500 pounds).
Large aircraft tend to be "working airplanes" in passenger or cargo service, and will be operating to/from busy terminals. They will therefore benefit substantially from TCAS, and the operators can theoretically afford to equip their fleets.

### Seating Capacity

Carrying more than 19 passengers further includes aircraft which may not be "large aircraft" but might be used as "working airplanes" in regular airline/commuter service carrying passengers (and would therefore benefit from TCAS, and theoretically be producing revenue to offset the cost of equipping them).

This roughly aligns with FAR 121.391 flight attendant requirements (Even relatively small aircraft - maximum payload of 7,500 pounds or less - are required to have a flight attendant on board to assist in evacuation in the event of an emergency, so it logically follows that such aircraft should be equipped with TCAS to avoid at least one possible type of emergency (mid-air collision).

As Federico pointed out, this is largely a cost/benefit trade off (nobody would argue for a flight attendant on a Cessna 150, similarly the TCAS safety features would be overkill for most Cessna 150s in the world).

• I wonder if the smallish jets (Citation, LJ 45, etc) might not benefit? Anyone know the general costs associated with TCAS? – CGCampbell May 24 '14 at 20:39
• @CGCampbell they probably could - nothing stopping people from installing a TCAS system in them except money (\$20,000 for the box, plus install - as of right now) – voretaq7 May 24 '14 at 21:01
• @CGCampbell Most Learjets and Citations have TCAS, although it is only required for turbine powered aircraft with 10 or more seats operating under 14 CFR 135. – Lnafziger May 25 '14 at 20:11
• Basically, they require it on aircraft that will in normal situations be used in airliner operations. There's nothing prohibiting it from being installed in any aircraft, as long as they want to pay for the electronics, and/or certification costs if the part has never been fitted to the type in question. Also, as a note there are a significant number of business jets that are large enough to be in the 5700kg weight range. – slookabill Feb 20 '15 at 23:18