Explanation Required: ATA (actual time of arr) and ATD (actual timeof dep)

Here is my definition.

- ATA means Touch Down Time (Wheels On the Ground)
-ATD means Take Off Time (Wheels Off the Ground)

-Chocks Off.. Parking Brake Released.. and Aircraft ready to push back
from Gate
-Chocks On.. Parking Brake Applied.. and Aircraft stopped at Gate

My definition of ATA / ATD is what I see being used in FIDS (Flight
Information Display Systems) in both BKK and HKG Airports.. by the
Civil Aviation Department. And, they use Chocks ON and Chocks OFF as
well.

However, I was told yesterday that, Airlines consider ATA and ATD to
be Chocks On and Chocks Off respectively.

Is this true? Why is that? Why give Chocks On the name ATA.. While
there is a already perfect name for it... which is Chocks On. and same
for ATD.

In my opinion again, ATA should be touch down time.. and Chocks On
should be Chocks On (that is arrived at Gate).

Please explain or give some official reference that conforms with what
I hear yesterday.

Thanks.

The best that I can think of is who is concerned with the information you are giving. When a GA aircraft gives ATA and ATD that allows others to see how long the aircraft is in flight. But on a commercial carrier the passengers don't care if they landed on time, they want to make sure they get off the plane when they are suppose to, so to allow for easier planning for customers airlines factor in taxi time for them. This isn't supported by any information, its just the most logical explanation I could think of.

On 9/17/2010 12:00 PM, SVCitian wrote:
Here is my definition.

- ATA means Touch Down Time (Wheels On the Ground)
-ATD means Take Off Time (Wheels Off the Ground)

-Chocks Off.. Parking Brake Released.. and Aircraft ready to push back
from Gate
-Chocks On.. Parking Brake Applied.. and Aircraft stopped at Gate

My definition of ATA / ATD is what I see being used in FIDS (Flight
Information Display Systems) in both BKK and HKG Airports.. by the
Civil Aviation Department. And, they use Chocks ON and Chocks OFF as
well.

However, I was told yesterday that, Airlines consider ATA and ATD to
be Chocks On and Chocks Off respectively.

Is this true? Why is that? Why give Chocks On the name ATA.. While
there is a already perfect name for it... which is Chocks On. and same
for ATD.

In my opinion again, ATA should be touch down time.. and Chocks On
should be Chocks On (that is arrived at Gate).

Please explain or give some official reference that conforms with what
I hear yesterday.

Thanks.

This is an opinion, not a quote from official sources:
1) A pilot certificate is required to taxi, and it may be logged as
flight time.
2) Airlines are now obliged to deboard passengers after a 4 hr (I think
it is) ground wait for takeoff - to avoid some of the 6,7,8,9 hour black
top hold debacles in previous years. So they are keenly interested in
establishing WHEN the clock starts.
Talk about meat packaging and transport!

Brian W