Most G1000 transponder implementations have an automatic ground switch. Then what?
Depends where you are. Some places don’t care, others (like for example Zürich, where you are supposed to squawk from clearance reception to on-block) will tell you to turn the transponder on again.
The issue isn’t ground verses air. It is standby verses Ground/Air. The ADSE-X systems use the transponder, but not in the normal way. The delay between an interrogation and a reply by the transponder is too great when on the ground, so multilateration is used on the reply to determine position. In the case of a mode S transponder, they will not respond to a mode A/C or all call interrogation when they are in ground mode, however they still squitter and respond to a mode S addressed interrogation. A mode S transponder sends different data when in ground mode than in airborne mode, so needs to be able to reply with the appropriate data. For a mode S transponder that is also ES capable with ADS-B Out, they need to broadcast (squitter) in ground mode and they also use different data. I discussed some of this with the fellow in the FAA who wrote the SAFO and told him they need to clarify what they are asking for as most aircraft use some sort of input such as weight on wheels or an airspeed switch or GPS groundspeed and altitude to change between ground and air status. What they don’t want is for the transponder to be turned off or switched by the pilot into a standby mode. Standby mode will not reply to anything. Ground mode will for a mode S transponder. In the case of a mode A/C transponder, the ground mode and standby are the same, not true for the mode S transponder.
Interesting. Like many others I was taught that it was supposedly a big issue if transponders were in ALT on the ground, because it would clutter the air traffic controller’s screens……..
I guess they’ve upgraded their software as well.
I’ve seen that several large airports (Stockholm/Arlanda being one) state in AIP that mode A/C transponders be kept off at all times on the ground , while mode S transponders should be kept on in ground mode because the airport has surface movement radar with mode S multilateration.
The G1000 handles this automatically.
Its all about the good airmanship, and CPL standard would be: entering runway, strobes on, landing light on, transponder alt, check the runway heading and off you go.
Yes, but you would sure want to do what the country’s or airport’s regulations say, not what some ATO sausage factory “taught” you, no?
It must be two or three decades since I intentionally changed the transponder setting from ALT. At one point, decades ago, ATC would ask one to turn off the transponder when on the ground, but the radar software, at least in the US, has long since ignored the ground returns. Since ASDE-X has been installed at the top 30 or 40 airports in the US, the requirement to leave the transponder on for ground operations has been around, usually announced as part of the ATIS. Some pilots with TAS units have objected to receiving ground alerts on their systems, but by now they should have adjusted to the expectation that traffic on the ground may be detected. Later design systems have better alerting algorithms. I have left my transponder on because it is one less thing to forget to do on departure. I also reject the OWT that leaving it on while on the ground will burn out the transponder or reduce its life.
I wouldn’t necessarily say sausage ATO factory as most of the checklist I have seen also use the same method just before departure. It’s a personal preference and to be honest some follow it some don’t. Of course if a certain country request or prefers to squawk alt on the ground thats fine. In major airports this can have a negative impact on older TCAS systems while on the ground. My Avidyne axp340 also recommends to squawk alt when airborne.
In the US, especially when installed with ADS-B active, the AXP340 STC requires a squat switch or automatic air/ground determination and will auto switch between GND mode and ALT mode. That satisfies the FAA for having the transponder in ALT at all times as GND mode is a variation of ALT. What does not satisfy the FAA is the unit is powered off or in SBY mode.
Here is what the AVX340 Pilot Guide says.
The possible states are as follows:
ALT – The transponder will respond to all interrogations.
ON – The transponder will respond to all interrogations, but altitude reporting is suppressed.
SBY – The transponder is on, but will not reply to any interrogations.
GND – The transponder will respond to Mode S ground interrogations from surface movement radar. This mode is only available in installations that send a ground/air discrete signal to transponder.
When airborne, the transponder should always be set to ALT unless otherwise directed by Air Traffic Control. Aircraft installations that include a ground/air state input (e.g. gear squat switch or wired discrete from a GPS/Nav/Com such as the IFD540) will automatically select GND on landing or while taxiing and will automatically select ALT when airborne. In these installations, the pilot selectable states are ALT-ON-SBY when in air and GND-SBY when on-ground.
Does anyone know about regulations that restrict use of mode “ON” or “ALT” while on the ground? (There is nothing in Part-SERA or ICAO doc 8168.)
Or has anyone been asked to turn off the transponder or to set GND or STBY while on the ground?
The reason for the question is that I fly several aircraft whose transponders automatically activates in mode A/C/S a short while after being switched on, although still on the ground.
I have always switched them back to STBY as soon as I saw that, just as I always switch to STBY after leaving the runway after landing.
But yesterday I flew with a pilot who told me that he has for years just ignored the problem, always left the transponders in mode A/C/S on the ground, and never had a single remark from ATC about it.
I know there is some filtering going on based on ground speed, in the ATC system, but what about TCAS in approaching/departing airliners?
These transponders are designed to switch to ALT on departure, based on either barometric pressure or GPS speed, but apparently the pressure gauge changes its output during warm-up, leading the logic to believe the aircraft has taken off when it has not, and so going “ALT”. The problem should be fixable by the radio shop, of course, but lengthy discussions with the local shops have not lead anywhere, apparently. Several years ago I changed the setup myself, trying to make the transponder disregard the pressure input, according to the maintenance manual, but I did not manage to solve the problem.
