Reply from Bureau of Transportation Statistics

[Mark Gobell]

I sent this to the BTS chaps:

[chek]

'Diverted' seems a suitably bureaucratic euphemism.

[Mark Gobell]

My follow up question to the BTS folk was:

[Mark Gobell]

[Mark Gobell]

The ACARS service provider at Dulles is ARINC

So what has the missing data got to do with AA not reporting?

[Mark Gobell]

So I sent his:

[conspiracy analyst]

Does someone press a button to transmit the data?
It occurs automatically from the moment a plane is in the air?
If the data wasn't transmitted that implies it did not exist.
There can be no other logical explanation.

[Mark Gobell]

I haven't looked into all the aspects of ACARS.

All I know atm is that ARINC is the data service provider for the ACARS system at Dulles.

They are saying that ACARS captures the data in real time and then transmits it to ARINC.

ARINC provides the facility for ACARS.

ARINC is ACARS at Dulles.

This seems not to make sense.

[Bushwacker]

What BTS must mean is that they are not sure if the data is transmitted to them in real time.

According to Wiki "One of the initial applications for ACARS was to automatically detect and report changes to the major flight phases (Out of the gate, Off the ground, On the ground and Into the Gate); referred to in the industry, as OOOI. These OOOI events were determined by algorithms in the ACARS MUs that used aircraft sensors (such as doors, parking brake and strut switch sensors) as inputs. At the start of each flight phase, the ACARS MU would transmit a digital message to the ground containing the flight phase, the time at which it occurred, and other related information such as fuel on board or origin and destination. These messages were primarily used to automate the payroll functions within an airline, where flight crews were paid different rates depending on the flight phase."
I suggest that a flight that produced a message via ACARS of taking off, but not landing, as hijacked and crashed planes would, would throw up an anomaly on the system which would call for human intervention to determine. UA and AA then corrected the anomaly in different ways, UA by showing the details and AA by deleting the record. Given that the whole point of the BTS database is to record the on-time performance of airlines, the AA staff presumably took the view that information about their flights was not relevant for the purpose, in the apparent absence of any specific guidance.

[Ningen]

I'm not seeing your argument, Bushwacker. Whether data transmission was real time or not, it would be transmitted to ARINC or BTS. Why would AA or UA be in a position to delete or not delete?

We know that BTS excluded all four flights from their statistics, because a hijacked plane that never landed would not be a fair input for a statistic on on-time landings. They could have left the takeoffs, I guess, but it's understandable they just excluded all data for the flights from the statistics.

So the anomaly was addressed at the statistical level for both airlines, but only AA is not shown in the data. Why?

Great work, Mark. BTS' explanation sounds contrived to me.

[Mark Gobell]

Your explanation fails also Bushy on the fact that neither AA11 or AA77 from different airports, originally had an actual take off time.

That was the point that started the whole mystery.

I can't see any way whatsoever that a carrier who uses ACARS exclusively, could also be in the loop of providing manual data to the airports ACARS Data Service Provider.

One statement contradicts the other does it not?

[Bushwacker]

I think what you are missing is that ACARS is primarily a system of communicating between the plane and the airline on the ground, not to provide information to BTS. The flight data goes to the airline, ARINC are simply the data carrier. Information passed on from the airline to third parties, such as BTS is the responsibility of the airline to provide. They may do it automatically from their system, or they may do it manually. BTS appear not to know whether they get real time information or not, but either way an anomaly would be reported by the system to the airline, not to BTS, and it would be for the airline to correct. UA did it one way, leaving in the take-offs with an explanation, AA did it another, deleting the information on the whole flight including take-offs.

[Mark Gobell]

Is that an op-ed piece or do you have a link?

[Mark Gobell]

Browsing ACARS related stuff and it seems that the ACARS data is sent to the carrier's own ground station.

[Mark Gobell]

What I still don't understand is why was the ACARS data was withheld for these aircraft.

If the ACARS data from the carrier's ground station isn't transmitted onwards from them in real time, as the BTS responses seem to imply, then it must go in batches at some later time.

Removing the data for one or two planes would require some kind of edit.