Watsonville Wave – Transponder Usage — Bay Area Soaring Associates

Watching Dan Colton’s video and reading his description of his 12/16/2017 wave flight over Watsonville brought back memories of the handful of similar flights I’ve had on north-wind wave days. His video shows the fantastic visibility you usually have in those conditions. But it sure is cold up there!

I really froze my ass off on one February flight when we were pointed north away from the sun for more than an hour to stay aimed into the wind, while we watched airliners pass beneath us on the way to SFO and SJC. Of course that meant we couldn’t see those airliners as they approached from behind the glider. And they probably couldn’t see us because gliders are just really hard to see until you get really close. Since visual traffic separation is of limited utility in those circumstances, we were both relying on a functioning transponder in the glider for Norcal Approach to keep the airliners separated from the gliders.

Airliner Routes

Just where are the airliner routes? I think most of the traffic coming into SFO from the south uses the SERFR TWO arrival route, while traffic from the south headed to SJC uses the SILCN FOUR arrival route. SERFR TWO arrivals pass over the Pleasure Point surf break just west of Capitola, crossing the EPICK waypoint between 10,000 and 15,000 MSL at 280 knots, continuing north directly over Eric Rupp’s house to disturb his peace. SILCN FOUR arrivals headed for SJC pass just west of San Juan Bautista, crossing the big open-pit quarry at Aromas where we often catch the north-wind wave. These arrivals cross the WLSSN waypoint just north of the A. R. Wilson Quarry at 8,000 MSL or above and 250 knots. Some of the SFO departures also turn south over the Santa Cruz Mountains and climb out above the arriving traffic. And keep in mind that airliners and business jets may be vectored off the standard routes by the controllers, for sequencing or other reasons.

On SkyVector.com, ForeFlight or your favorite aviation app you can look up these arrival procedures and also type in these waypoints on the Sectional Chart view to see where they are located. If you look on a flight-tracking website such as FlightAware.com, you can type in SJC or SFO to see the arrival traffic for those airports highlighted. A few minutes ago I watched a 737 on FlightAware cross the WLSSN waypoint at a little over 8,000 MSL with a groundspeed over 300 knots. If you were working the wave over the quarry at those altitudes and an airliner was approaching from behind you at over 300 knots, what are the odds they could visually acquire your little white glider in time to take evasive action?

Now that we have established that a functioning transponder is key for traffic separation in this busy airspace, how do you make sure your transponder is functioning correctly? We do have official transponder checks performed on BASA gliders by a technician on the ground, but that is only once every two years. As a pilot, however, you can call up Norcal Approach in flight for a transponder check. As long as you don’t interrupt them in the middle of another conversation, they are happy to oblige.

How do you call for a transponder check? First, use the correct frequency. The Norcal Approach Frequency over Watsonville is 127.150, while over Hollister it is 124.525. Above about 7,000 feet the frequency switches to 133.950, but it is probably best to make initial contact on 127.150 or 124.525 first regardless of your altitude, and they will hand you off to 133.950 if they think that is best. The quarry at Aromas is kind of on the border of these two sectors, but if I was calling from the quarry area or west of there, I would start on 127.15.

How to Get a Transponder Check

Once you have tuned in the correct Norcal frequency, listen. Listen some more. If you hear Norcal calling another aircraft, wait for that aircraft to respond. If you hear another aircraft calling Norcal, wait for Norcal to respond. When you are sure they have finished their exchange of calls, listen some more to make sure Norcal doesn’t have three more calls they need to make right away.
Use your full call sign upon the initial call-up. For example, “Glider 451CH”, rather than just “1CH”. Once the controller has used your full call sign in responding to you, you can in theory use an abbreviated call sign of the last three numbers and letters in your N number. But if in doubt or just when you feel a need for clarity, feel free to use your full call sign on later calls.
Once you have a clear spot on the airwaves, key the microphone and say: “Norcal Approach, glider 451CH requesting transponder check.”
Norcal will respond with something like: “Glider 451CH, Salinas altimeter 30.03, say position and altitude and ident.” “Ident” here means he wants you to push the Ident button on your transponder. This causes your aircraft display on his scope to light up, so he can be sure he has identified the correct aircraft on his scope.
In theory you are supposed to set your altimeter to the pressure setting they give you before reporting your altitude. But we don’t have our glider altimeters calibrated very often and I might just leave mine on the same setting it was when I took off – the Hollister setting is not likely to be very far off from the Salinas setting and the inaccuracy in my altimeter pressure window might be much greater than that difference.
You should acknowledge the altimeter setting the controller gave you (even if you aren’t going to use it), and respond with your altitude and position, using approximate bearing and distance from the nearest significant airport. Hollister and Watsonville are “significant” for this purpose, Bikle, Panoche and Frazier Lake are not. Don’t use a geographic reference such as “San Juan Bautista” or ‘Highway 101” because these features are not displayed on the controller’s radar scope. Round off your altitude to the nearest hundred feet, and always clearly separate thousands and hundreds in your altitude description. Your response call should be something like: “Glider 451CH is about five east of Watsonville airport climbing through six thousand niner hundred, squawking one two zero two, altimeter setting three zero point zero three.” For altitudes of ten thousand or above you say each digit separately, for example “one two thousand four hundred” instead of “twelve thousand four hundred”.
The controller will ask you to “Ident” either as part of his initial response to you or as a subsequent instruction. Push the Ident button on the transponder and say “identing”, either as part of your main response, or as a separate response like “Glider 1CH indenting” if the controller separately asks for an ident.
Once the controller has seen your ident she will say something like “Glider 1CH, radar contact 6 miles southeast of Watsonville airport at seven thousand one hundred.” As long as the altitude they see is within a few hundred feet of the altitude you see on the panel, then your transponder is considered to be working OK. If the reading is different from what you gave them but only because you are still climbing, you might respond with something like “That altitude checks for glider 1CH” or “Glider 1CH currently seven thousand one hundred” (assuming you are seeing the same altitude they are reporting for you). If the altitude you report is way off from what they see, they might tell you to “disable Mode C”, in which case you would turn the transponder switch from “Alt” to “On”. A big discrepancy in the readings indicates something is wrong with the altitude encoder, and you should report that to the ship captain if it’s a BASA glider.
What if you don’t get any response when you first call Norcal? The controller may be on the phone with another controller or a control tower, she may be in the middle of a shift change (in which case she is having a conversation with the controller who is about to take over that scope position), or she may be talking to another aircraft on another frequency. Wait a couple of minutes and then try again.
The controller might ask if you are requesting “radar advisories”. My response would generally be “No”, because if I accept radar advisories then:
1. I will need to input a new squawk code the controller gives me into the transponder
2. I will need to stay on the Norcal frequency rather than going back to 123.3
3. The traffic advisories he gives me may not make much sense because he will assume that the direction of my ground track indicates which way the nose of the glider is looking even if I’m going backwards over the ground, and
4. If the controller doesn’t understand what gliders can and cannot do, he may even give me vectors to fly taking me right out of the lift band, or ask me to maintain a particular altitude. If I was the only glider out flying that day I might try it just to see what happens, but I think it would be a learning experience for both me and the controller.
When the exchange regarding the transponder is finished, I would probably say something like: “Glider 451CH leaving the frequency, gliders will be on 123.3 if you want to contact us.”

That was a long explanation, but the whole process is really very simple and is usually done with in less than a minute.

Two More Thoughts

I’ve been to 17,999 a few times for the thrill of it, but now I usually stop my climb at 17,500 MSL or less. I have often left weak lift only to fly into strong lift, meaning if I leave weak lift at 17,999 I could easily go a few hundred feet above 18,000 just trying to leave the lift. In addition to that, my altimeter might be off by a few hundred feet. So I like to leave a reasonable margin below Class A airspace.

At 17,000 feet or so, the north wind might be blowing at 50 knots or more. Someone pointed out that if you had to bail out over Watsonville in those conditions, the wind would probably blow you well out into Monterey Bay before you reached the surface. Maybe, just maybe you could steer your parachute east and drift far enough southeast as you came down to stay over dry land. I haven’t been tempted to fly out over the ocean in north-wind wave since I thought about that.