ACARS automatic position reports
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Joined: Nov 2020
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From: Newcastle, NSW
ACARS automatic position reports
I have noticed a discussion on an aviation oriented website where there seems to be a difference of opinion on what is the source of latitude/longitude positions used for the ACARS automatic position reports used by airlines for operational scheduling purposes on the Boeing 777 200 series aircraft. I wonder if anyone might be able to shed some light on the issue.
I have paraphrased what was discussed as follows:
Some people think they originate from the aircraft's Flight Management Computer (FMC) that most of the time will favour the GPS as it is generally will give the most accurate position whilst others believe instead it originates solely from the aircraft's raw uncorrected data extracted direct from inertial reference system (On the Boeing 777 this is called the ADIRU).
Ideally apart from just opinions it would be good to back up any answer to this with some reference material e.g. Technical documentation, a letter from Boeing etc.
Also so pilots would know what are the side effects to any navigation system failure e.g. the ADIRU which provides raw uncorrected inertial reference positional data then if anyone can provide the correct answers to the following questions that would be great:
Q1 - What is the source of ACARS automatic position reports in regards to the latitude/longitude data?
(1) The Flight Management Computer.
(2) The raw uncorrected inertial reference data from the ADIRU.
Q2 - If after having an ADIRU failure and then after completing all the essential tasks first (e.g. when the SAARU takes over entering the aircraft's heading from the magnetic compass etc) which of the these three options apply:
Note as the ADIRU has failed there would be no raw IRS Latitude/Longitude data available.
(a) The automatic thirty minutes ACARS position reports would still be sent as per normal to the airline operations department as the Flight Management Computer (FMC) would obtain position information from the two GPS receivers. So you would not need to do anything extra.
(b) The automatic thirty minutes ACARS Latitude/Longitude position reports would still be sent to the airline operations department. However as the sole source of the positional data (Latitude/Longitude) was from the failed Air Data Inertial Reference Unit (ADIRU) the Latitude/Longitude fields would contain Null values. If time allows you might consider contacting the operations department from time to time to provide estimates for your arrival etc.
(c) The sole source of the positional data (Latitude/Longitude) was from the failed Air Data Inertial Reference Unit (ADIRU) so now as this is unavailable this will inhibit the automatic thirty minutes position reports being sent to the airline operations department. If time allows you might consider contacting the operations department from time to time to provide estimates for your arrival etc.
I have paraphrased what was discussed as follows:
Some people think they originate from the aircraft's Flight Management Computer (FMC) that most of the time will favour the GPS as it is generally will give the most accurate position whilst others believe instead it originates solely from the aircraft's raw uncorrected data extracted direct from inertial reference system (On the Boeing 777 this is called the ADIRU).
Ideally apart from just opinions it would be good to back up any answer to this with some reference material e.g. Technical documentation, a letter from Boeing etc.
Also so pilots would know what are the side effects to any navigation system failure e.g. the ADIRU which provides raw uncorrected inertial reference positional data then if anyone can provide the correct answers to the following questions that would be great:
Q1 - What is the source of ACARS automatic position reports in regards to the latitude/longitude data?
(1) The Flight Management Computer.
(2) The raw uncorrected inertial reference data from the ADIRU.
Q2 - If after having an ADIRU failure and then after completing all the essential tasks first (e.g. when the SAARU takes over entering the aircraft's heading from the magnetic compass etc) which of the these three options apply:
Note as the ADIRU has failed there would be no raw IRS Latitude/Longitude data available.
(a) The automatic thirty minutes ACARS position reports would still be sent as per normal to the airline operations department as the Flight Management Computer (FMC) would obtain position information from the two GPS receivers. So you would not need to do anything extra.
(b) The automatic thirty minutes ACARS Latitude/Longitude position reports would still be sent to the airline operations department. However as the sole source of the positional data (Latitude/Longitude) was from the failed Air Data Inertial Reference Unit (ADIRU) the Latitude/Longitude fields would contain Null values. If time allows you might consider contacting the operations department from time to time to provide estimates for your arrival etc.
(c) The sole source of the positional data (Latitude/Longitude) was from the failed Air Data Inertial Reference Unit (ADIRU) so now as this is unavailable this will inhibit the automatic thirty minutes position reports being sent to the airline operations department. If time allows you might consider contacting the operations department from time to time to provide estimates for your arrival etc.
