Transponder to standby

[squeakmail]

I have religiously turned my transponder to "standby" before changing the squawk code - and I've religious taught students to do the same.

Am I doing the right thing...or wasting my time (and theirs)?

Does a sweep of the radar cause garbled codes during number changing...or, to be more precise, does it matter to you guys (and gals).

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LIVE in peace...or REST in it!

[LoLevel]

depends on the Radar processor. Most take a couple of sweeps to process the data ...4-5 seconds depending on the type. But , strictly speaking you are doing the correct thing and it is good airmanship, especiall to miss those 77 codes.

[InspectorGadget]

...and those 76 and 75 !!!!!

By the way, it is good practice I think to do so, but when I fly I just spin through them quickly!!!

Aren't I the naughty one!

IG

[Capt Pit Bull]

I used to go to Standby before changing code.

These days however, I reckon its the lesser of two evils to leave it on.

As is mentioned in posts above, it probably won't cause a problem as the radar hardware will solve it.

It should also be considered that although you could cause a temporary error in your 4096 code, at least by keeping your transponder 'On' your Altitude Reporting data is still going out. This is important so that TCAS can operate correctly. By going to Standby you become invisible to the other guys TCAS.

Whilst I don't have any figures to prove it, having looked at TCAS incident reports I get the impression that the hand over from one controller to another is a risk factor. Since a change in squawk is part of the hand over process, it would seem sensible to ensure that your Altitude reporting is kept active. TCAS doesn't care about your 4096 code.

Any thoughts, anyone?

CPB

[aluminium persuader]

Kinda depends on how big a change it is, and what numbers you'll be going thru on the way. If you hit 77, 76 or 75 then your code as displayed on the tube starts flashing, alarms start beeping and the D&D cell at LATCC start getting excited.
If it's only a quick change (as others have said, no more than 4 or 5 secs) I wouldn't worry too much!

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Once more unto the breach, Dear Friends...

[need to know]

Is it not possible to keep one transponder on one code while selecting the newly assigned code on the second transponder. I dont have a huge amount of airline knowledge but this would seem like common sense. This way you get to keep your readout for TCAS while not setting off emergency codes or activating the code of another aircraft. When you have correctly selected the newly assigned code, then switch transponders??????

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And that's what I think about that.

[fireflybob]

Not this one again.
Friend of mine (pilot) did exhaustive research and discovered that it is NOT necessary to select standby when changing transponder codes - as has been previously stated the mode charlie needs to be left on for TCAS, etc.
Obviously you should not take all day about changing codes but so long as you select the new code in a "normal" manner there is no problem.
In short, no need to select standby.

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[Flybywyre]

I also do the same as squeakmail and have often wondered whether anybody else does,however,I think I will not bother anymore as the ATC software requires two hits before capture and recognition. There is one scenario that could create a problem, that is if you get distracted before you have completed the change.On reflection I think I will continue the practice of turning to standby.Will you continue to teach your students the same?

[Feather #3]

FBW et al,

May I respectfully suggest that you DON'T turn the transponder to SBY when changing squawk.

In modern ATC centre's, selection of SBY will remove your target/data from the screen until the computer has a few sweeps to fit you back into the system. It will continue to track a "live" transponder while the numbers alter in a sort of 'memory' mode while the squawk changes to look for a new number and database reference.

Thus, if the centre is not one which processes raw data [and few do these days outside a TMA], you can very inconveniently disappear off the screen on selection of SBY.

Is that what you or the ATCO looking after your interests really want?? http://www.pprune.org/ubb/NonCGI/eek.gif

G'day

[squeakmail]

Ooo, er, missus!!

Are we now saying that turning it ON will take two or three sweeps of radar to acknowledge that it is there...but turning it OFF is instant lack of data?

Looking back through the messages it seems that TCAS is the thing we are trying to protect...rather than ATC confusion.

I was surprised to see mention of "code change" on handover...I would have thought (although, presumably, incorrectly) that at the levels where heavy metal meets PA28...all code changes would be finished and the little guy (me...hence the reference to teaching students) would already be identified and locked into the airspace system that the heavy metal deems to be theirs (and only theirs).

On the question of "Will I still teach that way?"...to be honest, I don't know. I'll probably - as I do with many aviation thingies - show 'Gromit' (I don't fly with Bloggs anymore) both ways, discuss the comments and options and let him/her suit himself/herself in the future. Whatever I tell him/her...I may be wrong.

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LIVE in peace...or REST in it!

[bird on the wire]

I have to say that I thought it was all a bit much ado about nothing until my 170a flight test for my instrument rating. I was changing xpndr codes (on standby ).
I glanced down to check the code before I switched the thing on and blow me if I didn't find the thing reading 7700 and an examiner waiting expectantly...

The chances must have been quite a lot to one, but I have been a convert to changing to standby when changing codes ever since

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they bought their tickets - they knew what they were getting into

[Flybywyre]

Thanks for the advice Feather # 3

Your comments are interesting and I will think about them over the next couple of days. I'm not sure disappearing for a couple of sweeps is such a problem, especially as ATC will presumably expect this to happen.

It would be interesting to know what the manufacturers recommend, anybody got any information?

[Fokjok]

First, the point about changing codes 'on the other transponder' might be worth considering, but most aircraft I have flown have two transponders drivenm by one selector head, so only one code is ever displayed - you just select which box (and which Mode C feed) is active.

Second, it is my understanding that whilst ATC radars do take their time to receive and process SSR transmissions, the same is not true of airborne radar as used in SAR, for example on the British Nimrod, which does (I am told) show an emergency squawk on first reception. Would a Nimrod crew-member care to comment... perhaps someone at LATCC could make a 'phone call to ask the question....

[need to know]

Ok FOKJOK. Point taken about the two transponders. But after ATC advise you of a new transpondser code, how long does it take to input such a code?Surely it's just a case of twiddling a few numbers. Why the confusion? I ask purely from a learning point of view????

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And that's what I think about that.

[squeakmail]

If the debate takes the track of "two transponders"...can we steer it back to the point of view that ALL aircraft could benefit from an answer...not just airliners.

Remember, there are more PA28's on the UK register than ANY other aircraft type...and I doub't any one of them has a spare transponder...nor a "non handling pilot" to "twiddle the numbers" whilst the handling pilot scans the TCAS.

Please, don't forget your roots when continuing this discussion.

[need to know]

Sorry if you thought I was going off the point squeakmail. I thought it would have been obvious by me saying the Question asked was from a learning perspective that my "ROOTS" are not in the left seat or the right seat but in a seat outside the aircraft. Hence the question.

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And that's what I think about that.

[Flybywyre]

I'm at work (LATCC) tommorrow morning so I will pop into the military and ask about the SAR radar as mentioned by Fokjok. Regarding the point made about the importance of TCAS and maintaining the continuity of transmission, it is worth remembering that most PA28's, which is where this thread began, allthough fitted with SSR are not mode C enabled.

[Feather #3]

To comment on a couple of posts:

Squeaks; Although I drive B744's for a crust [loaf even?], during any year I fly a variety of a/c down to the lovely DH-82A [Ahhh! de Havilland!!] The same technique applies to all; simply change the numbers while squawking.

However, if you DO operate in an environment with Jurassic radar systems, the old technique may apply. I would respectfully suggest that most Western world systems now rely on computer processing of SSR data, and that my earlier comments are valid.

FBW; Please don't perpetrate the myth they've tried here in Aust that you MUST have Mode C [Altitude reporting] to be any use to TCAS. A basic transponder still alerts the crew to your position. It may not give height [naturally], but helps the eyeballs to scan in the right direction. If you have a transponder, turn it on to your country's basic VFR squawk [as a minimum] EVERY time you are airborne! Please!!

G'day

[Capt Pit Bull]

Need to know,

regarding setting the code on the other transponder, and then changing over.

It depends on avionics fit. Even in an aircraft with two tranponders, it may not be possible to set the code on the transponder not in use. Although you may have 2 tranponder boxes in the rack, often they are operated by a single control head. This would have a toggle switch to change between 1 and 2, but only one set of code setting knobs. Does that make sense?

I.E. you can't change the code on the box not in use.


If I can just reiterate for those who are clinging to the 'Standby' method, please don't do it. Even if your transponder is at standby for say 5 seconds that is still a large proportion of the alert time thresholds for TCAS at low levels. If you are really worried about inadvertantly selecting an emergency code, it pretty easy to avoid going via 77, 76, or 7500. You're much more likely to get caught out by the single push 'squawk emergency' or memory features that some control heads have.


CPB

[Flybywyre]

What are you talking about feather#3.....
Jurasic radar? old technique? You've obviously spent too much time in that glass cockpit that you fly.....try a bit of real flying in the real world. Oh, by the way, next time you are sitting at the controls of your 747, in between cups of coffee I would respectfully suggest you brush up on TCAS operations....which ONLY works on mode C interrogation.
Back to the real world.
I spoke to D&D at LATCC this morning who were pleased this subject has been mentioned as pilots who change squawk without going to standby mode are the bane of their lives. The chaps there were very helpfull and made three important points.

1. D&D (SAR) radar is no different from any other radar. Two hits will be required for capture.
2. ALLWAYS turn to standby when changing codes to avoid setting SAR alarms off, which happens on a regular basis due to pilots using the "Ausie" method of just changing the numbers.
3. When the SAR alarm is set off, that screen is then out of action untill the matter has been resolved thus creating a small delay should a real emergency code be transmitted.

They also mentioned that since 7000 was introduced they get far more erroneous alarms as two aircraft changing to 7000 without going to standby in close proximity can trigger the alarm. Apparantly this is quite common around the Solent area.
They informed me that there is talk of reverting back to the old 4321 conspicuity code.
It may be helpfull to draw a line between GA traffic pottering about VFR and airways traffic who will not be squawking 7000. It is the GA traffic that can cause a problem when changing without reverting to standby.
D&D are now aware of this site and may well talk to us in more detail if requested.

[This message has been edited by Flybywyre (edited 05 May 2000).]

[Self Loading Freight]

Just as a point of information -- do all transponders use thumbwheel switches or one-button-per-digit? While these were common in certain classes of radio equipment a few years back, as far as I'm aware most such applications now use a keypad plus some form of execute/load button.

That has the advantage that you can't select an intermediate code while you're changing the settings, but does mean that if you don't press the execute button properly you're left thinking that the code displayed has been accepted while the equipment is still using the old one. Good user interface design (UID) can minimise the chance of this happening, through a number of strategies.

I'dve thought that in any case better UID could sort out this problem, leaving the transponder active on the old setting during the process of changing the code while ensuring the code IS changed safely, even during very busy or choppy times. In this particular case, the fact that the safety aspects are so pressing and that both modes of use -- going to standby during change, or leaving it active -- have their downsides makes me think that this is a good case for getting some kind of fix into the works.

R

[Feather #3]

FBW,

Thanks for a summary of your visit to the D&D chap.

Would you mind next time at the office, popping in to your supervisor and or techs and asking them what would happen if everybody in the UK FIR's switched their transponder to standby when changing squawk?

Would this suit the overall operation or not?

BTW, have a careful read of my precise words on TCAS. I didn't teach the use for a number of years to be taken for granted.

G'day

[This message has been edited by Feather #3 (edited 05 May 2000).]

[LoLevel]

Interesting Thread.
Hadn't considered the push-button SSR type.
Along the same vane..... :)

What is o/s (non-oz) view on ACFT sel TXPDR ON/ALT before entering the active RWY? And what about when crossing an Active runway during taxy out? Also...what are your company procedures for TCAS mode selection whilst in the TMA or close prox to AD?
[email protected]
http://www.highabove.com/images/logo/logo.gif www.highabove.com (http://www.highabove.com)


[This message has been edited by LoLevel (edited 06 May 2000).]

[This message has been edited by LoLevel (edited 06 May 2000).]

[Flybywyre]

Feather # 3

I'm back to LATCC on Wednesday when I will put your question to Tech's.
Unless of course one of them drops into this forum and can advise accordingly.

FBW

[aluminium persuader]

Since SSR will rarely pick up a squawk from the ground (at my place, I'm lucky if it picks it up from 500'!), I would say not necessarily b4 you enter the active, but certainly yes please definately b4 you roll. I'm also ppl/me/imc used to work for Air Service Training (remember them?) at EGPT. Last 3 chks on the runway b4 roll were txpr - alt
strobes - on
rwy - clear.
Something I always stick to.
Consider this; A/c recovering on RAS to ILS at busy class G airfield, a/c 2 gets airborne to depart 3/4 upwind vfr, but not yet switched on txpr...OOPS AVOIDING ACTION!!!
How am I the radar controller supposed to know that the primary blip is remaining at 1000' if he's not wearing the squawk I gave him?
I give squawks for a reason (not just to ease my nerves), but anyway, doesn't the Good Book say somethin about
"Txpr-equipped a/c are to squawk 7000 + mode C from t/o to t/d unless instructed to squawk a discrete code issued by an ATSU, the exeptions being a/c in emergency (natch) and a/c remaining in the visual circuit (txpr to s'by)
http://www.pprune.org/ubb/NonCGI/eek.gif


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Once more unto the breach, Dear Friends...

[Corporate Yank]

Interesting question, "Turn x-ponder to standby when changing codes"? Back to the books. Our King Air is equipped with dual Collins TDR-94 mode-S units. Upon any change to the code selection, the control head waits approx 5 seconds before resuming squawk. I have to believe that most units today have this feature.-CY

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*deep inhale* I LOVE the smell of jet-a in the morning..

[Capt Pit Bull]

Corporate Yank,

As a matter of interest, does the manual say whether it stops replying to all interrogations, or just Mode A All Call (i.e. the one which asks for the 4096 code).

CPB

[sirocco]

From an ATC's point of view, pilots SHOULD select transponder to standby prior to changing the assigned code!

The reason is that in the process of changing the code, the radar may sweep and pick up an intermediate code which has been assigned to another aircraft. Alternatively a wrong code could be selected, and be transmitted prior to the error being realised by the pilot. This could cause an erroneous code/callsign coupling. This is particularly a problem with the newer ATS systems which display flight plan, ADS and radar tracks, as a pilot squawking the wrong code can cause the deletion of the aircraft symbol of a lower hierarchy (eg: a flight plan track).

Of course, transponders and radar systems do have features to mitigate these risks, but they don't seem to work...

[Corporate Yank]

Here it is verbatim...The Ctl head waits approx. 5 sec. before sending the new code to the transponder. This provides time for verification of the selected code before it is transmitted and prevents inadvertant transmission of a partially set code. For 7700 & 7600, the display (Ctl Head) flashes the code for 5 sec. before sending the code to the transponder.--CY

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*deep inhale* I LOVE the smell of jet-a in the morning..

[Feather #3]

"just when you thought it was safe to come out..................................!"

Airservices Australia have just issued a Notam shooting down my previous argument [which was based on Euro/US data.]

They have decided that transponders should be selected to SBY prior to squawk change if you have a 'tumbler' selection unit as you may trigger someone else's code and confuse the system.

Life wasn't meant to be easy!!

G'day

[Low_and_Slow]

<font face="Verdana, Arial, Helvetica" size="2">I have to say that I thought it was all a bit much ado about nothing until my 170a flight test for my instrument rating. I was changing xpndr codes (on standby ).
I glanced down to check the code before I switched the thing on and blow me if I didn't find the thing reading 7700 and an examiner waiting expectantly...</font>

All this really argues for is care in changing codes. I never turn mine off (but then mine is 20 years old and likely the switch would fall off if I did). I'm just carefull not to turn the first digit through 7.

-me

[eyeinthesky]

The initial question seemed to be whether good airmanship dictated that turning the transponder to standby would prevent wrong squawks showing on radar. That seems sensible, especially when you think (as many of you don't seem to be) that we are talking about student pilots with twiddly knob transponders and an information overload. It is not as simple as you airliner types with two transponders and push buttons. It seems a good starting point from which you can progress when you start moving to push button or two transponders etc.

From an ATC point of view we have a system called Auto-DM which recognises the squawk assigned to a flight in the computer. Within certain parameters, if the computer sees that squawk it will activate the flight. If you have by chance selected the squawk in error then the computer will produce flight strips, estimates etc for a flight which is not yet airborne. The plan will then need to be cancelled and re-input. OK so the chances are small, but we are in the business of minimising chances of error, so if you can do that by selecting standby then what's stopping you?

I will certainly continue to teach my students to squawk standby, especially as some of them take 30 seconds or more to finish twiddling the buttons!



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"Take-off is optional, Landing is mandatory"

[DeltaTango]

If it's all te same to the tubes then it's just another trap in your work load,as small as it might be.

:)DT

[matspart3]

Single engine, single crew, IMC, no autopilot
my technique (as taught by a great instructor)is stanby-scan-twiddle-scan-twiddle-scan-check-scan-squawk and txpndr only goes on during after take off checks to avoid unnecessary garbling in the circuit area. Probably very different in Class A and a Jumbo but that's my twopenneth. ATCOing at a non SSR unit, with lots of puddle jumpers we get lots of calls from D&D about misdialled 7700's

[cossack]

Whose idea was 7000 for conspicuity?
Only one click away from SOS.

What's wrong with 1200?

How many times have you dialled up your slot time in your transponder and forgot to change it? Why do you do that? Don't you have a pen?

As eyeinthesky said, false autoDM on an incorrect squawk is very common. I reckon I have to get a pilot to change squawk after departure at least once an hour!

To standby or not standby, I don't mind.

Just set it right!

[HugMonster]

I agree - I think 7000 for conspicuity was a very silly idea.

Our aircrafts' TXPDRs (Collins) are the same as Corporate Yank's - they switch themselves to standby when you twiddle until five seconds after the last input.

I appreciate the controllers' points of view regarding problems over briefly selecting a code that might trigger a flight plan, but for TCAS point of view, however long it takes (within reason) I would prefer to have my TXPDR interrogating another's.

Okay, the first might well be thoroughly inconvenient. The second might be thoroughly dangerous! And let's face it, whilst we're trying to avoid errors, we're also trying FIRST AND FOREMOST to eliminate danger.

So let's have those transponders on (please?)

As a sideline, I would also prefer use of a transponder Mode C mandatory. So often controllers pass us "Slow-moving traffic your twelve o'clock, no height information". If we're under a RAS and can't see it, he HAS to give us avoiding action, even though the chances are it's more than 10,000 below.

So instructors, please teach your studes to use Mode C at all times.