# Tag Info

## Hot answers tagged arinc-429

16

There is actually quite a lot of difference between ARINC-429 and MIL-STD-1553. They are different because they were developed by two different groups with different needs. Both started in the 1970's. Before then there was almost no digital data of any kind on a an aircraft. It was almost all analog or discrete. The biggest issue was noise and ...

8

In the example you pasted, the value $1.5_{10}$ is being sent, which has binary representation $1.1_{2}$. The data is sent as an unsigned integer so some kind of multiplier needs to be applied. The value occupies 19 bits, at offset 11 within the packet itself being bit 0 of the data. The default multiplier is such that the "units" bit (ie the one ...

6

The receiver has to be programmed. It's important to remember that A429 is a unidirectional hard-wired bus with a single transmitter and multiple receivers. Each connection is physically unique and the reason for all the pin-out diagrams and bus definitions in the ARINC Characteristics. To help with data integrity and fault detection, each transmitter ...

6

It's an error. Attachment 2B does show that label 204 from the GNLU (Equip ID 056) and GLU (Equip ID 060) as being in knots (highlighted below). That is not correct, it is a BNR in feet as shown for Air Data System (ID 006) and ADIRU (ID 038). Knots only applies to Label 204 from the FMS (ID 002). It's still incorrect in A429 P1-18, March 2012. ARINC ...

6

Your basic decoding strategy looks correct -I didn't double-check the values, but the logic is sound. Note, however, that the difference of BCD vs two's-complement is not the only difference between BNR and BCD (and Discrete labels, which are also common). Binary-coded decimal (BCD) and binary (BNR) labels generally do decode as you have shown, but the Sign-...

5

ARINC 429 is a defined standard that not only describes the packet structure (32 bits) but also the data formats for different labels depending on the equipment ID. To know how to properly decode an ARINC 429 label you need to know the Equipment ID, which can then be used to look up the meaning of a specific label. The manufacturer of the device that the ...

5

The example given is a bit strange in that it explains how to code a specific value as the scaling factor changes. In using A429, we don't often think in terms of how the scaling factor modifies the coding of a specific value as the range (scale) is fixed for any specific A429 label. To code a value, we look at the what the data type is and the range/...

4

ARINC 429 is a unidirectional one-to-many (broadcast) transfer bus with a maximum of 20 receivers. SourceDesign with four unidirectional ARINC 429 buses There is normally little need to identify the source, as there is only one. So there is no field in the protocol word dedicated for ID transmission. As visible in the previous image, bidirectional ...

4

FAA Order 8260.46F - Departure Procedure (DP) Program describes "... the policy, guidance, and standardization for initiating, developing, processing, and managing the Departure Procedure (DP) Program." Your questions are broad-based, but Order 8260.46F should provide the answers you are looking for. Here are two figures from Order 8260.46F. These ...

4

There is no defined "calibrated altitude". The following are all altitude related labels: 102 Selected Altitude, 107 Selected Cruise Altitude, 120 Range to Altitude, 127 Selected Landing Altitude, 131 Intruder Altitude, 144 Altitude Error, 153 Max Altitude, 162 Density Altitude, 164 Min Descent Altitude (MDA), 203 Altitude, 204 Baro Corrected Altitude #1 &...

3

You asked the question in terms of ARINC 424 which imposes the constraints of the database structure and use. So I'll try to explain SIDs within that constraint and in the broader sense. The reason for that is that ARINC 424 exists to support the use of an FMS (or an RNAV navigator). But some SIDs don't require an FMS to fly them. The ones that start with "...

3

Is it possible to communicate an everyday computer with the ARINC bus? Sure. there are appropriate controllers to be plugged in a slot - or even as USB, like the one you found. After all, basic USB is alread way faster than ARINC 429. If so, what is the access point where we would connect the wire? Whatever connector the interface card/box offers. More ...

3

I'm not 100% sure about ARINC definitions specifically, but in the general aeronautics usage the inertial frame is the ground (flat Earth) frame. The rotation from this inertial ground frame to the body frame is defined by what is known as Euler angles. Consequently, the inertial angular rates are Euler rates: the rates at which the Euler angles change. In ...

3

The first thing you need to understand is that DMEs are not tuned by their actual frequency but by the frequency of the paired VOR/VHF Com, ILS, or MLS frequency. For the vast majority of operations, this means a VOR or ILS frequency. This frequency as well as mode settings are coded in the Label 035 as shown below: And the text from reference to Section ...

3

In A429 BNR words bit 29 is the sign bit. Individual label descriptions are not entirely consistent in that many will identify bit 29 as part of the sig bits field. In any case it's important to look at the details of a specific label, especially the range, MSB, and LSB values. Some are always positive (such as airspeed) and so the sign bit is assumed to ...

3

It depends on which ARINC document you're talking about. ARINC 429 is a digital serial bus standard. Discrete data may be sent in ARINC 429 data words, but that's just bits in a word not the physical discretes you're asking about. ARINC also has documents that cover standards for other interfaces as well as 'Characteristics' that define specific LRUs such ...

3

Resolutions in the A429 spec are approximate, so calculate them yourself. Resolution = Range / (2^significant bits) Here is one way to do it: Load your 32 bits into a signed 32-bit integer. Shift left 3 so the sign bit is now in bit 32. Shift right (32-significant bits)-1 to form a 2's complement "fixed-point" number. Convert to float and multiply by the ...

2

The mistake I think the link is making is that number of significant bits determines the position of the LSB. The scale factor can influence the necessary number of sig bits, but the desired resolution does as well. The easiest way I've found to calculate the value that actually gets inserted into the label is as follows: The scale factor (which I'll call \$...

2

From ARINC 429, Attachment 6: Label 025, Selected Altitude (BCD) Five binary coded decimals. Range is up to 50000. Resolution is 1 foot. Bit 29 (MSC) ------------------------------ Bit 11 (LSC) 4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1 1 0 0 | 0 0 0 1 | 0 0 0 0 | 0 0 0 0 | 0 0 0 0 The above line codes to 41000 ft. Note: Negative ...

2

The general ARINC guideline for publishing data is to publish both BCD and BNR values when both types are defined. That allows the receiver of the data decide which to use. If only one form exists, then that's the way it's coded. It ultimately comes down to what the ARINC committee decided made the most sense. Typically, BNR coded data is used by ...

2

The ARINC 429 Word resolution tells you what value the LSB corresponds to. You can also tell what the resolution should be by looking at the Range and Significant Bits. It doesn't describe the actual electrical signal.

2

Yes, a SID can have three parts as you described. The runway transition defines the path from each runway to get to the common route section of the SID. All runways then share the common route section. After the common route, there may be multiple enroute transtions to get an aircraft on to the rest of its flight plan. Below is the EPKEE RNAV departure from ...

2

On modern aircraft all equipments that needs to communicate to each other in binary format may use ARINC 429 protocol. For instance all fly by wires computers on Airbus 320, 330, 340 use arinc 429 protocol. Nowadays other protocols do exist too such as arinc 629 protocol or fiber optic protocols etc. As a summary all aircraft systems that need to transmit ...

1

DeltaLima very nicely covered the "what" of these labels. As to the "why", I have three examples of their uses: Autopilot setpoints (altitude, airspeed, heading) are displayed on the Primary Flight Display for the pilot's situational awareness (and so that she knows when to stop when twiddling the autopilot control knobs) They can be logged to a Flight Data ...

1

Both labels are used to transmit the altitude and airspeed that are dialed into the Mode Control Panel of the autopilot. They are not necessarily the current altitude/airspeed, instead they are the target values that the autopilot is steering to.

1

From what I can see, the "true" static pressure is the measured static pressure corrected for airspeed & position (Static Source Error Correction). In my copy of ARINC 429 (May 2004) I don't see a label definition that fits this "true static pressure". Label 171 can be used for manufacturer defined data, so I would see if you can get a better answer ...

1

As you may notice from this spec tutorial or this errata report, the two bits that serve as a "sign-status" field for BCD data show only status, not sign, for BNR data. The status codes for BNR data include a "failure warning" code; it is not necessary to signal a failure warning in the sign-status matrix of BCD data because the individual digits can be set ...

1

ARINC 429 is both an electrical bus standard and a data standard. The electrical standard defines a unidirectional, one to many (Tx to Rx) serial data bus that is transmitted using bipolar Return to Zero (RtZ). This makes the signal self clocking. If no data is being transmitted, the line stays at 0 VDC (Null) which consequently removes the clock as well. ...

1

That is normal for an ARINC 429 receiver. The clocking for ARINC 429 is built into the transmission data, with the bipolar Return to Zero format having a Null for the last half of each bit time and requiring 4 bit times of null (0) voltage between labels. This lets the receiver adjust to the data rate automatically.

1

Short answer: No easy way. It may be possible for a crew to detect some drift by comparing the IRS mag heading to the magnetic compass. This does have problems though as the IRS doesn't really 'measure' mag heading. It works in true heading and calculates mag heading by applying a magvar correction from a table. Modern aircraft do not have free gyros that ...

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