What causes a stuck mike?

AuntPeggy

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Last night, Hubby and I were returning from a day of flying.

Hubby had been flying with his instructor, working toward getting his own CFI by "teaching" steep turns and other maneuvers. I had been picked up in the morning by a "jet jock" who was flying one of the King Airs up for its annual to Harriman and West (AQW) in Massachusets. He offered me a ride in the right seat since there would not be any passengers. Following his lesson, Hubby flew up to give us both a ride home while "teaching" our friend how to fly.

Ceilings were very low and it was certainly an adventure picking our way through and beneath low clouds that were touching occasional mountain peaks. Jonathan phoned Hubby to say we had arrived and that he had picked up some ice coming through the clouds, so between them they decided that Hubby would make the trip from Poughkeepsie (POU) to AQW by flying under the clouds and between the peaks.

Turbulence that had blown the King Air about and bounced me in my seat had an even stronger effect on our C-172. Strong gusty winds were swirling around and over mountains and valleys. Hubby was bounced around mercilessly and despite my cinched seatbelt, after we all took off, my head tested the strength of the ceiling covering by bouncing up into it with quite a bit of force. It was kind of scary even with two of the best pilots I know in the front two seats.

After dropping off our friend at White Plains (HPN), Hubby and I proceeded to take the 172 home to Bridgeport (BDR).

We were on downwind when suddenly, there was a loud rushing sound in my headset and I heard Hubby's voice come through the air (not through the headset) asking, "Can you hear me?"

"No," I said since I knew he wanted to know if I was hearing him from the headset. "Can you hear me?" I didn't hear if he responded. He pointed to the red light on the intercom that said we were transmitting. He turned off the intercom and then turned it back on, but there was no improvement. He clicked his mike button a few times. I clicked mine, too. No change. By this time, he had completed downwind and base and turned final. "Were you cleared to land?" I wondered out loud.

"Yes, I was cleared on downwind," he replied. He could hear me just fine. Then tower offered, Stuck mike on tower. Had tower heard me?

Without keying the mike, I replied, "We're trying to fix it." At that moment, the red light went out and the loud rushing sound stopped and I could once again hear Hubby from my headset. We were able to taxi to parking without any radio problems.

Now, I'm wondering, what happened?
 
"Yes, I was cleared on downwind," he replied. He could hear me just fine. Then tower offered, Stuck mike on tower. Had tower heard me?

Without keying the mike, I replied, "We're trying to fix it." At that moment, the red light went out and the loud rushing sound stopped and I could once again hear Hubby from my headset. We were able to taxi to parking without any radio problems.

Now, I'm wondering, what happened?
How did you hear the tower if your mic was stuck on? If you are transmitting that would mean your receiver was muted and you would not hear anything anyone else was transmitting.

The other thing is that from your description it seems as though you are talking about the intercom red light not the transmit light on the radio if so equipped?

If you are indeed speaking of the intercom red light, that would just indicate that the intercom squelch level has been exceeded. If your intercom is like mince that is user adjustable with a knob near the intercom volume. Exceeding intercom squelch does not affect transmit over the radio at all. It does however let you hear what ever the mics are picking up at that time.
 
How did you hear the tower if your mic was stuck on? If you are transmitting that would mean your receiver was muted and you would not hear anything anyone else was transmitting.
I wondered that, too.

The other thing is that from your description it seems as though you are talking about the intercom red light not the transmit light on the radio if so equipped?
Right. There is a "T" on the G530, but I don't remember whether it was on.

If you are indeed speaking of the intercom red light, that would just indicate that the intercom squelch level has been exceeded. If your intercom is like mince that is user adjustable with a knob near the intercom volume. Exceeding intercom squelch does not affect transmit over the radio at all. It does however let you hear what ever the mics are picking up at that time.
We hadn't messed with the squelch. And tower noticed a stuck mike, so I'm sure that was at least part of the problem.
 
Should we ground the plane until a mechanic has looked at it?
 
I'll post a scenario. Somebody ELSE'S mike was stuck and you were hearing the carrier ("rushing sound") from THEIR transmitter. For whatever reason, your intercom picked up that rushing sound and opened the squelch on your intercom (red light).

You could hear the tower clear you to land because at that point in time the tower was closer to you than the the aircraft with the stuck mike and overpowered the stuck mike radio.

As to your original question about what causes stuck mike, there are a dozen components in the chain between your PTT switch and the radio's transmitter that could fail and cause "stuck mike". The most common is a loose nut on the pilot's seat that sticks the microphone between his or her legs so that she or he doesn't have to reach for it.

Jim
 
Quoting: "Then tower offered, Stuck mike on tower."

Was the tower's mic stuck? That would explain the rushing sound as described above - it overcame the squelch so you heard a rushing sound. It would also explain how you heard the tower - they were still transmitting. It also explains why you had no further problems - it was the tower.

Maybe?
John
 
on older electronic work, i've seen one of the wires soldered to the PTT switch come loose, short to the other wire, and bypass the PTT completely. vibration can make this an intermittent condition and/or make the PTT work normally on occasion. metal fatigue usually causes the wire to break right at the solder connection.
 
I'll post a scenario. Somebody ELSE'S mike was stuck and you were hearing the carrier ("rushing sound") from THEIR transmitter. For whatever reason, your intercom picked up that rushing sound and opened the squelch on your intercom (red light).

You could hear the tower clear you to land because at that point in time the tower was closer to you than the the aircraft with the stuck mike and overpowered the stuck mike radio.

As to your original question about what causes stuck mike, there are a dozen components in the chain between your PTT switch and the radio's transmitter that could fail and cause "stuck mike". The most common is a loose nut on the pilot's seat that sticks the microphone between his or her legs so that she or he doesn't have to reach for it.

Jim
Quoting: "Then tower offered, Stuck mike on tower."

Was the tower's mic stuck? That would explain the rushing sound as described above - it overcame the squelch so you heard a rushing sound. It would also explain how you heard the tower - they were still transmitting. It also explains why you had no further problems - it was the tower.

Maybe?
John
The red light on the intercom indicates that we were transmitting.
 
The red light on the intercom indicates that we were transmitting.

The red light on the intercom indicates that the power to the red light was on. It is SUPPOSED to indicate that you are transmitting, but the only real way to know that you are transmitting is with a field strength meter loosely coupled to your antenna.

If you really were transmitting, there is no known failure mechanism to let your receiver hear anything in transmit mode, not even if your TR relay was broken. The receiver, even if the TR changeover voltage mechanism failed, would be so blown away from a 10 watt source a few inches away from the receiver input that there is no way in the world for a transmitter a mile or so away would overcome that close-coupled source.

Jim
 
Gremlin. Keep an eye on it, see if it happens again. If it does, look into it more carefully.

I was flying through the area yesterday - I heard reports that it was bad, but I must have missed all the bad parts, worst I got was light chop.
 
Sunday was intense in the area....flew N66 (Oneonta) to KPOU couldn't find any smoooth air over the hills. First time I ever saw 158kts GS going eastbound. winds were 320/45 with gusts. Two hands on the plane kinda day.
 
The red light on the intercom indicates that the power to the red light was on. It is SUPPOSED to indicate that you are transmitting, but the only real way to know that you are transmitting is with a field strength meter loosely coupled to your antenna.

If you really were transmitting, there is no known failure mechanism to let your receiver hear anything in transmit mode, not even if your TR relay was broken. The receiver, even if the TR changeover voltage mechanism failed, would be so blown away from a 10 watt source a few inches away from the receiver input that there is no way in the world for a transmitter a mile or so away would overcome that close-coupled source.

Jim

I think the red light on an intercom means squelch was broken, and only the indicator on your actual radio indicates it's transmitting.
 
The red light on the intercom indicates that the power to the red light was on. It is SUPPOSED to indicate that you are transmitting, but the only real way to know that you are transmitting is with a field strength meter loosely coupled to your antenna.

If you really were transmitting, there is no known failure mechanism to let your receiver hear anything in transmit mode, not even if your TR relay was broken. The receiver, even if the TR changeover voltage mechanism failed, would be so blown away from a 10 watt source a few inches away from the receiver input that there is no way in the world for a transmitter a mile or so away would overcome that close-coupled source.

Jim

The function of the red light on the intercom depends on the intercom. Some use different colors to indicate transmission vs reception and/or open intercom squelch. I haven't read any mention of the intercom model in question here. And any transmit indicator on the intercom (baring a failure in the intercom) normally indicates that the Mic Key line from the intercom to the audio panel (or radio) is grounded (which is what happens when you push the PTT). Unless that wire is broken or there's something wrong with the radio the chances are very high that the radio is transmitting when the intercom indicates the Mic Key is active (grounded).

I do agree that if the comm radio in an airplane is actually transmitting you're not going to be able to hear any transmissions from outside the plane. OTOH, you would normally hear your own voice (but not anyone else's on the intercom).
 
I would only ground the plane if the 530 "tx" indicator was lighting uncommanded.

Until then I'd arch an eyebrow at it only, and wait for it to cause trouble again. Also, grounding the plane is harsh, it could be a headset, mic jack, or any number of non-plane gremlins too.

If it acted up again, I'd power off the 530 and switch to my standby comm -- if the problem persisted, it's almost certainly wiring upstream of the audio panel. You could also try unplugging one headset, or switching the jacks you were using, in an effort to isolate the problem -- workload and situation permitting of course.

$0.02

- Mike
 
As a troubleshooting step you can do if it occurs again.

If you have a Pilot Isolate switch on your intercom, does switching to it disable the Copilots PTT switch?. This might allow to keep using the radio if the copilot PTT is sticking.

Also pushing switch that is actually sticking will often dislodge it.

Brian
 
A stuck Mike usually occurs when Michael isn't paying attention and steps into curing concrete or quicksand.
 
Aunt Peggy, do you keep your plane at BDR? That is Sikorski, right? Do you know someone there who probably rides a Harley, the one he rode when we were up there was green, he may have gotten another, but he's in a club with a 172 out of there. His last name is O'Keefe...

We used to live in Orange but when we moved down here to Memphis we lost touch with him.
 
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