TRANSPONDER - STBY or AUTO?

HHAS · December 18th, 2007, 22:51

Dear Controllers,

I am in need of some clarification as far as ATC is concerned.

The Chief Pilot of our carrier has devised a SOP policy that requires the following:

Because of the routes we fly, various radar controls will issue us new squawk code and changes enroute.

The SOP requires us to first put the transponder on STANDBY before entering the code then back to AUTO upon entry of the new squawk code.
My question is from a controller's operational standpoint, is it neccessary to put the transponder on STANDBY or can the NEW squawk code while the transponder is transmitting

For a controller's system does it make a difference

PLEASE ADVISE

Thanks in advance.

mnixon · December 18th, 2007, 22:56

I think it has more to do with the transponders memory in case of power failure. In some models, if you put the new code in with it in ALT and then have power failure to the unit, it will reset to the last saved code.

OldTownPilot · December 18th, 2007, 23:33

Or would it have to do with accidently squaking one of the "bad codes" for a radar pass as you were changing the number?

Fox Xray · December 19th, 2007, 00:16

I dunno... if an A/C needs a code the wrong code splits time with the speed in the data block. I know nothing about transponders... as long as you get the code in that should be fine.

ghogue · December 19th, 2007, 01:06

Well, here's my take on this. The AIM in my opinion says not to squawk STBY during code changes. It does not say that directly, but by implication.

4-1-19. Transponder Operation

3. Civil and military transponders should be adjusted to the "on" or normal operating position as late as practicable prior to takeoff and to "off" or "standby" as soon as practicable after completing landing roll, unless the change to "standby" has been accomplished previously at the request of ATC. IN ALL CASES, WHILE IN CONTROLLED AIRSPACE EACH PILOT OPERATING AN AIRCRAFT EQUIPPED WITH AN OPERABLE ATC TRANSPONDER MAINTAINED IN ACCORDANCE WITH 14 CFR SECTION 91.413 SHALL OPERATE THE TRANSPONDER, INCLUDING MODE C IF INSTALLED, ON THE APPROPRIATE CODE OR AS ASSIGNED BY ATC. IN CLASS G AIRSPACE, THE TRANSPONDER SHOULD BE OPERATING WHILE AIRBORNE UNLESS OTHERWISE REQUESTED BY ATC.

and,

e. Code Changes

1. When making routine code changes, pilots should avoid inadvertent selection of Codes 7500, 7600 or 7700 thereby causing momentary false alarms at automated ground facilities. For example, when switching from Code 2700 to Code 7200, switch first to 2200 then to 7200, NOT to 7700 and then 7200. This procedure applies to nondiscrete Code 7500 and all discrete codes in the 7600 and 7700 series (i.e., 7600-7677, 7700-7777) which will trigger special indicators in automated facilities. Only nondiscrete Code 7500 will be decoded as the hijack code.

In saying to avoid inadvertent selection of certain codes and using the examples they give, it implies you're to remain "on" during code changes.

One more important fact worth mentioning. Even though you might only be in STBY for a few seconds, ATC would lose radar contact with you during that period (perhaps not a big problem, I don't know), but more importantly, you would render TCAS inoperative during this time.

gary

Cptnchia · December 19th, 2007, 12:19

Quote:

Originally Posted by ghogue

4-1-19. Transponder Operation

3. Civil and military transponders should be adjusted to the "on" or normal operating position as late as practicable prior to takeoff and to "off" or "standby" as soon as practicable after completing landing roll, unless the change to "standby" has been accomplished previously at the request of ATC.

Unless of course you're flying out of ATL or the other handful of other airports which require your transponder to be on while taxing on the airport.

BajtheJino · December 19th, 2007, 12:38

At every company I've worked for we kept our transponders on ALT at all times unless asked to do otherwise. I can't imagine why you boss would ask you do that unless the manufacturer has deemed it neccesary.

Velocipede · December 19th, 2007, 12:41

Sounds like your Chief Pilot is from the "olden days" before solid state radios. Back then, you went to STBY to lift the points off the radio crystals so you wouldn't damage them. Solid state avionics changed all that...in the 60's.

ghogue · December 19th, 2007, 17:29

Quote:

Originally Posted by Cptnchia

Unless of course you're flying out of ATL or the other handful of other airports which require your transponder to be on while taxing on the airport.

Yeah. I wasn't going to go there since the OP was about changing codes in flight.

rickyrhodesii · December 19th, 2007, 20:09

It's always amusing to watch a pilot with the old dial transponder spin the numbers in. If they're really slow, you can watch the numbers change on the scope.

sharkey · December 19th, 2007, 20:54

Today I had a controler tell me "check transponder, you appear to be squaking standby." For the record we weren't; but I thought you couldn't see us when we were on standby.

Towerboss · December 19th, 2007, 22:17

Yes we can tell when you are squawking stndby.

HHAS · December 19th, 2007, 22:25

Thanks for the quick reply folks.

Perhaps some clarification is due.

We operate the B767/200-300 and the transponder utilizes a NUMBER PAD entry sytem which is similiar to a phone and upon receipt of sqwauk code we punch in the S code, it's NOT a DIAL switch that would inadvertently transmit a distress or emergency signal as we are toggling thru the various numbers etc.

PilotChip · December 20th, 2007, 02:02

Everybody just squawk low then we wouldn't have this problem...

TFaudree_ERAU · December 20th, 2007, 20:56

Quote:

Originally Posted by PilotChip

Everybody just squawk low then we wouldn't have this problem...

The transponder in our LJ55 has STBY/ALT/LOW. What the heck does LOW do? I mistakenly set it to LOW (its the top switch position; ALT is in the middle) one flight and didn't get any indication that it caused a problem.

Fox Xray · December 21st, 2007, 17:14

Quote:

Originally Posted by HHAS

Thanks for the quick reply folks.

Perhaps some clarification is due.

We operate the B767/200-300 and the transponder utilizes a NUMBER PAD entry sytem which is similiar to a phone and upon receipt of sqwauk code we punch in the S code, it's NOT a DIAL switch that would inadvertently transmit a distress or emergency signal as we are toggling thru the various numbers etc.

From your original post I assumed you were flying older equipment, I had no idea you were operating B767's. I'm sure you do not want to say what company this is but from what I understand there is no reason to squawk standby, depending on how fast you go to the new code your radar track could go into coast # ... meaning no flight plan tracking.

I don't understand why the chief pilot wants standby squawked for a code change ???

wildfreightess · December 23rd, 2007, 00:15

If your chief pilot is like our CP, he's probably like Velo said - he probably "grew up" with this procedure and just never saw fit to change once the necessity to do so became obsolete.

w5cdt · January 2nd, 2008, 22:39

Quote:

Originally Posted by Towerboss

Yes we can tell when you are squawking stndby.

Interesting...I thought STDBY was just the "warm-up" position and
no replies to interrogations were being made. So maybe you can tell
when we are in STDBY because you only get a primary echo? yes/no?

Minuteman · January 3rd, 2008, 00:40

Quote:

Originally Posted by HHAS

Because of the routes we fly, various radar controls will issue us new squawk code and changes enroute.

The SOP requires us to first put the transponder on STANDBY before entering the code then back to AUTO upon entry of the new squawk code.
My question is from a controller's operational standpoint, is it neccessary to put the transponder on STANDBY or can the NEW squawk code while the transponder is transmitting

Just going from memory, but I'd guess that SOP has more to do with the transponder than ATC.

I think one of the contributory factors in the GOL/Legacy crash in Brazil last year was that the Legacy's XPDR was in STBY. The SOP may be an attempt to encourage monitoring of the transponder and prevent repeated squawk changes from being interpreted as an RMP fault, potentially causing at least one brand of transponder to go into standby mode.

Towerboss · January 3rd, 2008, 00:41

Quote:

Originally Posted by w5cdt

Interesting...I thought STDBY was just the "warm-up" position and
no replies to interrogations were being made. So maybe you can tell
when we are in STDBY because you only get a primary echo? yes/no?

Yes we still get a primary.

TB

falconvalley · January 3rd, 2008, 02:54

Quote:

Originally Posted by rickyrhodesii

It's always amusing to watch a pilot with the old dial transponder spin the numbers in. If they're really slow, you can watch the numbers change on the scope.

LOL that's awesome. I've always wondered what that looked like on the controllers' end.

matteo · April 12th, 2008, 12:14

so how should we teach our students to operate transponders? a couple of us at my flight school have difference of opinions. some say we should leave them on alt all the time, out of sight, out of mind so you wont forget to switch to alt... some say that's a bad habit and you can forget to squawk the right code if you always leave it on alt?

any thoughts?

Bumblebee · April 12th, 2008, 12:40

Quote:

Originally Posted by matteo

so how should we teach our students to operate transponders? a couple of us at my flight school have difference of opinions. some say we should leave them on alt all the time, out of sight, out of mind so you wont forget to switch to alt... some say that's a bad habit and you can forget to squawk the right code if you always leave it on alt?

any thoughts?

sure . . .to those who believe that leaving the transponder on all the time to avoid forgetting it (even though it's on the checklist) I would submit that you should leave your strobes and landing lights on all the time as well, along with keeping the mixture in a rich setting. These all occur at the same time, at the same point in the checklist. If they forget to do the alt setting, they are not reading the checklist prior to takeoff and may miss these items also.
If this works logically then you have your answer.
respectfully submitted,
Dale

Chief Captain · April 12th, 2008, 18:49

Quote:

Originally Posted by HHAS

We operate the B767/200-300 and the transponder utilizes a NUMBER PAD entry sytem which is similiar to a phone and upon receipt of sqwauk code we punch in the S code, it's NOT a DIAL switch that would inadvertently transmit a distress or emergency signal as we are toggling thru the various numbers etc.

I'm pretty sure that those newer boxes have a delay built in when the new code is entered. Just keep it in AUTO, and enter the new code, and after a delay (~5s) it starts to reply with this new code. There's no real reason to go STBY, as if you enter an incomplete code, it will revert to the last valid code.