Tuesday, December 02, 2008

What if ATC asks you to recycle your transponder *

What the phased "recycle your transponder,"  tells you generically is that there is a "problem" and the controller needs you to do some trouble shooting. Per the ATC manager when you hear "recycle your transponder,"  99% of the time the controller is telling you that he does not have your Mode C readout.  

First thing the pilot should do is check that the transponder ON?
Second is it set to ALT?

When you hear "recycle your transponder" and the transponder is on, set to ALT,  ask the controller a question or two.
1.) Do you have my primary target? (meaning can the controller see you on radar on a horizontal plane, with no vertical i.e. altitude info.)
2.) Do you have a primary target but no mode C?
3.) Can you see me at all?

In the G1000 the transponder should already be on set to ALT,  when the equipment is functioning properly.
If ATC tell you they are only missing your mode C, just recycle the four digits. If you are squawking 1200, just retype or redial 1200.

In the G1000 check the soft keys, is it set to  STBY, ON, or ALT?  If you can't get the mode C funtion reset by retyping the digits set it to STBY then reset back to ALT.

Here are two sample photos of transponder antennas. On  airplanes you will see one of these types of antennas, inverted, on the airplane belly. They are UHF antennas, very short. If you see two UHF antennas on the belly, one will be a transponder antenna, the other a DME antenna.
ant pic


ant pic

Preflight your antenna:
These antenna are placed on the belly of the airplane, behind the engine and they collect oil and grim. Pilots need to check the transponder antenna and determine if the antenna is secure and clean.  If it is grimy, GENTLY wipe it off with the oil rag. Never yank on the antenna. Inspecting, and cleaning the transponder antenna when required, should be a part of every pre-flight.

If during your flight you think you may have a transponder problem here are some things to think about and some things to help you vet the problem.

Make sure the transponder is set to the “ALT” mode.

Did you ever wonder why some transponder mode selector knobs have many positions? The C172S airplane transponders selector knob has 5 positions, OFF/SBY/TST/ON/ALT.
OFF = Box is off.
SBY = Standby power to enables code selection.
TST = Self-test function, the transmitter is disabled. All display segments are illuminate.
ON = Enables the box to transmit MODE A (airplane I.D.) reply pulses only.
ALT = Enables MODE A and MODE C (altitude reporting).

A transponder needs to warm up before it can be effective; it can take between three and six minutes for it to warm up when placed in the ALT mode.

If you have a situation where ATC says to you, “Your transponder appears inop,” you need to make sure it is set to the ALT mode. If it is OFF, you ought confess to ATC that it was OFF. Turn it to ALT and tell ATC it may take a few minutes before they get a signal. Ask them to report when they pick up your signal.

Some people will recycle a transponder. But what does this mean? It means different things to different people. To some it means turning the box to OFF and then back to ALT. When you do this the warm up cycle will begin again and it isn’t useful. You may have to wait 3 minutes for the box to cycle fully on. Some people think recycling means resetting the 4 digit code in the transponder box. If ATC suggests you recycle your transponder you may ask them to clarify what it is they want.

If your transponder is set to “ALT” do a bit of trouble shooting. I suggest you fly at or above 1,200' AGL and then ask ATC for a transponder readout. If ATC still reports a problem ask for more info:
You can ask these questions:
-“Do you see me at all? ”or “Do you have primary target?” Primary target means they can see you (MODE A) but they do not have an altitude readout for you.
-“Are you getting a MODE C readout?” which means, is my altitude encoder working. If they say yes, ask them, “What is my altitude readout?” It should be within a few hundred feet. Always round up or down to the nearest hundreds of feet, do not report in tenths.

If time permits request a frequency change to a different controlling agency to verify the report. For example, if KPAO tower reports a problem, verify it with NORCAL. If both agencies report the same problem, this will help maintenance when they trouble shoot the Squawk.

However, if one agency says you have a problem but a second agency says you do not have a problem, you might not have a problem. The problem might be with the equipment of the first controlling agency. If you Squawk a transponder in this instance you might be sending maintenance on an expensive wild-goose-chase.

If a problem was reported during your flight where are some things you can do and think about after landing. Check the antenna. If the antenna is grimy please wipe it off. On the Aircraft Condition sheet report what ATC said, state what you did and what was observed. If the antenna was dirty, state that it was dirty and tell us if you wiped it down after your flight. Ask the next pilot to confirm the discrepancy. To guarantee you are aware of all written discrepancies you need to check the Maintenances Status Board before every flight.

If you confirm a problem with two controlling agencies when you were at or above 1,200’ AGL and the antenna is clean when you land, Squawk and ground the airplane.

If you do not confirm with two controlling agencies and you were not at or above 1,200’ AGL, you may not have gotten accurate information.  If this is the case, please don’t ground the airplane. In this case write an Aircraft Condition report that might look like this: “KPAO reported MODE C appears inop, flew only in pattern at KPAO, 800’AGL and lower. Did not confirm with any other controlling agency. Next pilot please confirm discrepancy.”

If you do a “confirmation flight” and no problem is observed please note that on the Aircraft Condition report. You might write something along the lines of, “Per KPAO tower and NORCAL approach, transponder function was normal.”

We are operating in a very complex environment with some very sophisticated equipment. We need to do our best to understand our equipment. 

*this was taken from the newsletter of a flying club I am affiliated with, there is a lot of communication from the Chief pilot to mechanic to the pilots, I am always learning!