Flarm collision alert from Tow Plane ADS-B

On Monday, March 19, 2018 at 3:52:28 PM UTC-5, Mike Schumann wrote:

The FARs require that all transponder equipped aircraft have their transponders turned on whenever they are airborne.

Actually, no; as Dan has pointed out, when aircraft are in formation (which is a specific case - not just a bunch of aircraft in the same area, like a gaggle), only the flight lead is supposed to have his transponder on; the rest are supposed to be in standby. In pre-Mode S days this was essential as multiple Mode 3s responding in the same area at the same time would overwhelm the SSR system at worst and trigger all sorts of collision alarms at best.

When the formation breaks up, the wingmen are then supposed to turn on their transponders. Releasing from tow is breaking up the tow formation, so...

This applies to all military and civilian formation flights.

Kirk
66

On Tuesday, March 20, 2018 at 7:10:48 AM UTC-7, kirk.stant wrote:
On Monday, March 19, 2018 at 3:52:28 PM UTC-5, Mike Schumann wrote:

The FARs require that all transponder equipped aircraft have their transponders turned on whenever they are airborne.

Actually, no; as Dan has pointed out, when aircraft are in formation (which is a specific case - not just a bunch of aircraft in the same area, like a gaggle), only the flight lead is supposed to have his transponder on; the rest are supposed to be in standby. In pre-Mode S days this was essential as multiple Mode 3s responding in the same area at the same time would overwhelm the SSR system at worst and trigger all sorts of collision alarms at best.

When the formation breaks up, the wingmen are then supposed to turn on their transponders. Releasing from tow is breaking up the tow formation, so....

This applies to all military and civilian formation flights.

Kirk
66

The technical need for the leader only squawking is partially folklore by now. Modern radar can decorelate multiple overlapping Mode C only targets, and absolutely see multiple Mode S targets. A direct result of the S for selective interrogation in the Mode S name. Wether an ATC controller might prefer to see one target for a formation flight, and not want to have spurious warnings on their display is a different question.

When I've asked Reno area NORCAL TRACON folks if they would want "formation flights" of gliders or GA aircraft to only squawk leader they said no.

ADS-B Out goes even further and targets will not "step on each other".

I would not be turning off any transponder or ADS-B Out systems unless specifically instructed to by ATC or you had a prior arrangement with them where it has been made clear they want this. And unsure, ask them.

On Tuesday, March 20, 2018 at 10:13:23 AM UTC-5, Darryl Ramm wrote:
On Tuesday, March 20, 2018 at 7:10:48 AM UTC-7, kirk.stant wrote:
On Monday, March 19, 2018 at 3:52:28 PM UTC-5, Mike Schumann wrote:

The FARs require that all transponder equipped aircraft have their transponders turned on whenever they are airborne.

Actually, no; as Dan has pointed out, when aircraft are in formation (which is a specific case - not just a bunch of aircraft in the same area, like a gaggle), only the flight lead is supposed to have his transponder on; the rest are supposed to be in standby. In pre-Mode S days this was essential as multiple Mode 3s responding in the same area at the same time would overwhelm the SSR system at worst and trigger all sorts of collision alarms at best.

When the formation breaks up, the wingmen are then supposed to turn on their transponders. Releasing from tow is breaking up the tow formation, so...

This applies to all military and civilian formation flights.

Kirk
66

The technical need for the leader only squawking is partially folklore by now. Modern radar can decorelate multiple overlapping Mode C only targets, and absolutely see multiple Mode S targets. A direct result of the S for selective interrogation in the Mode S name. Wether an ATC controller might prefer to see one target for a formation flight, and not want to have spurious warnings on their display is a different question.

When I've asked Reno area NORCAL TRACON folks if they would want "formation flights" of gliders or GA aircraft to only squawk leader they said no.

ADS-B Out goes even further and targets will not "step on each other".

I would not be turning off any transponder or ADS-B Out systems unless specifically instructed to by ATC or you had a prior arrangement with them where it has been made clear they want this. And unsure, ask them.

Understood - that's why I used the caveat "pre-Mode S". But the problem still applies if you have a Mode C backing up your ADS-B, right? And definitely still applies to most military jets until they all get updated to Mode S/ADS-B.

As usual, the devil is in the details - how many civilian flights or all-glider flight are really "formations"? Towing is about the only common (?) case, and that is not usually going very high or into congested airspace.

I seriously doubt ATW would want everyone in a 16-ship formation of RV-6s to have their Mode 3/C on!

Kirk