sábado, 20 de abril de 2013

Analyzing some details of the fatal mid-air collision: Adherence to Flight Plan

Our last post has stirred some reactions, as well as some comments.
This is excellent news – as discussing a problem/issue always means that knowledge and “awareness” is gained and views are exchanged.

The group of the association of the families and friends of Flight 1907 has commented the following:

We believe you have failed to consider a detail as the initial flight plan of GOL WAS 41000 feet. And they have asked permission and were cleared at 37000 ft on this route. So, there was no flight plan at 37000 for this route. The Legacy – according its flight plan – should have been at 36000 on this route. They didn’t ask for and didn’t receive clearance to change level. So they would have been at 36 and Gol would be at 37. They simply didn’t follow the flight plan. Furthermore 37000 ft in direction of Manaus is OPPOSITE TO THE FLOW of the AIRWAY.

So, let’s technically analyze some of these points made by the president of this association:

What is a Flight Plan (FPL)?

It is a specified information provided to air traffic services units, relative to an intended flight or portion of a flight of an aircraft (ICAO Annex 2 / ICAO Doc 4444).

The difficulty starts as “Flight Plan” has many meanings and definitions (by ICAO).

There are several flight plan types:

Filed Flight Plan (FPL).
Flight Plan Filed in the Air (AFIL).
Supplementary Flight Plan (SPL)
Actual Flight Plan (AFL)
Current Flight Plan (CPL)
Repetitive Flight Plan (RPL)

The Filed Flight Plan is the flight plan as filed (deposited) by the pilot in command, the aircraft dispatcher, or any other mandated agency/agent.

A Current flight plan (CPL) is a filed flight plan with amendments and clearances included (e.g. in flight and in two-way contact with ATC).

An Actual Flight plan is amended and corrected by time – according to the estimates and the progress of the flight.

A repetitive flight plan may be used for IFR flights with a high degree of stability over the same days of consecutive weeks on at least 10 occasions.



A good example of the difference between FPL (filed flight plan) and current flight plan (CPL) is what happened with flight GLO 1907 with Centro Amazônico of Manaus.

They had requested FL 410 in the FPL/RPL, but the pilots have requested FL 370 instead of 41000 ft via radio. So, clearance was given to climb to 37000 ft only = CFL = Current Flight Plan. And the Manaus controllers have changed and adapted the flight plan in their ATC – system (X-4000) accordingly.

Now, for N600XL the same has occurred:

NOVEMBER SIX ZERO ZERO X-RAY LIMA
ATC CLEARENCE TO EDUARDOGOMES, FLIGHT LEVEL THREE SEVEN ZERO DIRECT POÇOS DE CALDAS, SQUAWK TRANSPONDER CODE FOUR FIVE SEVEN FOUR, AFTER TAKE-OFF PERFORM ORENDEPARTURE”

This is by now the current flight plan (CPL) as cleared by ATC.
The FPL (which was filed is “amended”). The flight plan was adapted and “corrected” by ATC – this is now the valid and current flight plan.

CENIPA writes the following in its final report:

It is common that, when duly authorized by ATC, aircraft maintain flight levels different from the recommended standard and, provided there is not a conflict, controllers may authorize such procedures for the benefit of the traffic flow. Therefore, flying in a direction opposite to the normal traffic flow would not be incorrect, provided a coordination was made by the controllers and pilots, prior to performing such a procedure.

Our comment:

Yes, and we believe the following has happened with the Brazilian ATC-system:
The above clearance was issued by SBSJ TWR (following a telephone-coordination between Brasilia ACC).
FL 370 until Manaus was cleared, but the Filed Flight Plan (FPL) was not correctly updated/amended to become a CFL (Current Flight Plan) in the ATC-system. So, the Flight Data Processing System (FDPS) of Brasilia and X-4000 remained in the “ancient” state – FPL-state, and so not updated and/or corrected. This is also the reason why the ATC-system started to change automatically (and erroneously) the levels of N600XL after BRS.

This is what is called a “systemic error”. True, it’s for sure a non-error tolerant system-design.

For the operation of flights, ICAO says the following:

An aircraft shall adhere to the …

current flight plan; or
the applicable portion of a current flight plan; or
the applicable portion of a current flight plan submitted for a controlled flight unless

a request for change has been made and clearance obtained from the appropriate air traffic control unit; or

………………. unless an emergency situation arises which necessitate immediate action by the aircraft, in which event, as soon as circumstances permit, after such emergency authority is exercised, the appropriate ATS unit shall be notified of the action taken, and that this action has been taken under emergency authority.

In the US/FAA the following is valid and applicable:

(i) The altitude or flight level assigned in the last ATC clearance received;


Our conclusion: It’s untrue to say that the pilots of N600XL didn’t follow their Flight Plan.

And one aspect which we will discuss in a future post is the comment that N600XL flew "contra mão" - opposite direction, as the Brazilian love to say.

But can you fly "contra mão" in a radar sector - where "vigilâcia radar" is provided and guaranteed.
And so flights are "under radar ontrol" and are "identified" and "sob vigilância radar?

……………. More to come! Interesting discussions lying ahead of us! And comments are always welcome!

ATC Brasil

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