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Mode S Barometric Pressure Setting (BPS).

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Mode S Barometric Pressure Setting (BPS).

Old 18th Jan 2012, 04:31
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Mode S Barometric Pressure Setting (BPS).

Need somebody who can guide us in obatining more information on Mode S EHS transponders that automatically provide particular flight deck parameters to air traffic systems.

The Mode S EHS technology makes it possible for aircraft to downlink the flight deck altimeter setting in the form of a Mode S parameter known as Barometric Pressure Setting (BPS) The contact details listed on the NATS website appears no longer valid.
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Old 18th Jan 2012, 07:03
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A good place to start is the Eurocontrol Mode S homepage. Specific information for each transponder model can only be given by the manufacturer.

However BPS is not a reported mode S ELS or EHS parameter from what i can see there.

Last edited by Denti; 18th Jan 2012 at 07:16.
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Old 18th Jan 2012, 07:28
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BPS is one of the parameters sent in the EHS Selected Vertical Intention interrogation response, along with Selected Altitude (both visible to controllers) and various MCP/FCU mode parameter bits.

We routinely capture EHS data as part of a much larger monitoring project, let me know if you need to go into more detail.
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Old 18th Jan 2012, 08:22
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From 2018, aircraft with an MTOW >5700 kg or max cruise speed > 250 Kts will have to send BPS on ADS-B.

For Mode S I don't know the regulations by heart, but if I remember correctly, EHS is at the moment mandatory in some countries for certain aircraft categories.

What information are you looking for? Do you need information on specific transponder models or are you looking for certification standards, mandates etc.
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Old 18th Jan 2012, 11:15
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In order to apply the Barometric Pressure Setting (BPS) Advisory Tool, is a software upgrade required for the radar processing systems or is the information (incorrect altitude settings) send via downlink and processed like any data link information?
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Old 18th Jan 2012, 11:25
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In order to apply the Barometric Pressure Setting (BPS) Advisory Tool, is a software upgrade required for the radar processing systems or is the information (incorrect altitude settings) send via downlink and processed like any data link information?
I don't know, you'd have to ask NATS.

There's a good write-up on Mode S BPS here: http://www.skybrary.aero/bookshelf/books/1401.pdf.
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Old 21st Jan 2012, 22:52
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The Barometric Pressure Setting (BPS) on the aircraft is downlinked to the ground in the Comm-B date regiser (BDS 4,0) as Selected Flight Level / Selected Altitude. It is purely a reading from the baro setting, the transponder is unable to validate whether the value entered is correct for the airspace or level being flown.

It requires a software tool within or attached to the radar data processing at the ATC Centre or Tower to take that information and compare it to what BPS setting should be, i.e above transition should be 1013, below transition should be a QNH. The automated system would do the comparison and alert accordingly.

All level 2 and above Mode S transponders (i.e any sold in or operated in Europe) are capable of delivering the BDS 4,0 register if requested by a ground surveillance system - whether it has an appropriate interface or the aircraft can provide that information is a different matter.

RS
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Old 21st Jan 2012, 23:06
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next step

On aircraft fitted with digital ADC (s),

just how does the encoding altimeter (s) receive ALT info......

Reason for asking is that in the event of all Pitots / statics being blocked, can atc still display aircract altitude.....

Thanks

glf
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Old 22nd Jan 2012, 01:57
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Via the ADCs. On our type we select the transponder and the ADC of the flying pilot active, that way it shows the same information available to the acting pilot.
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Old 22nd Jan 2012, 09:03
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The Barometric Pressure Setting (BPS) on the aircraft is downlinked to the ground in the Comm-B date regiser (BDS 4,0) as Selected Flight Level / Selected Altitude. It is purely a reading from the baro setting, the transponder is unable to validate whether the value entered is correct for the airspace or level being flown.
That said, all the Airbus types (except the A380) and the Fokker 70/100 suffer from a bug which means that the last used QNH value is sent as the BPS even above the TA, instead of 1013.2.

Presumably fixing this isn't considered a high priority as the BPS value being sent is irrelevant when flying at a FL.
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Old 22nd Jan 2012, 22:58
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Reason for asking is that in the event of all Pitots / statics being blocked, can atc still display aircract altitude.....
ATC displays will show the same altitude as in the cockpit, so in case of blocked static ports/ dirty RVSM critical area / ADC out of calibration , the wrong altitude will be displayed to both flight crew and ATC.


Presumably fixing this isn't considered a high priority as the BPS value being sent is irrelevant when flying at a FL.
But it IS relevant when flying a FL. It still happens that flight crews forget to switch to QNE during the climb. Isn't the whole point of the advisory tool to alert the ATCO in these cases?
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Old 23rd Jan 2012, 06:34
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But it IS relevant when flying a FL. It still happens that flight crews forget to switch to QNE during the climb. Isn't the whole point of the advisory tool to alert the ATCO in these cases?
Sorry - you're right of course. What I should have said is that the altitude data being sent by Mode S isn't affected by whether the BPS is QNE or QNH.

In fact NATS have acknowledge the potential wider use of the BPSAT above the TA:

"The benefit of this tool is currently limited to detecting altimeter setting errors below the transition altitude. The tool has the potential to deliver much greater benefit if Airbus and Fokker updated their implementation of Mode-S BPS such that downlinked data reflected when flight crews are using the standard pressure setting above the transition altitude."
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