Wednesday, June 2, 2010

2006 Mid-Air Collision Brazil (re-posted)

Embraer Legacy 600 
Photographed by Adrian Pingstone 

For your information, what  follows is a re-posting of the previous four part post by combining the four posts into just one post.     
Since I brought up the subject of mid-air collisions in my last post, I thought it might be appropriate to look at this particular example of a recent one.  I have been following the developments of the investigation of this mid-air collision that took place in the airspace of Brazil on September 29, 2006, almost four years ago.

The fact the Internet has made a lot more information easily available is taken for granted today.  If I attempted to gather information concerning this specific accident which happened in Brazil without the Internet, I would have most likely given up.

In particular, I used three internet sources for the majority of my information.  Wikipedia was my most used site however the richest source was the 280 page Accident Investigation Report by the Brazilian Air Force.

The third source was the most dramatic source since it contained the actual cockpit voice recorder recordings of both aircraft. This source was an article titled "The Devil at 37,000 Feet" that appeared on the Vanity Fair Magazine's web site written by Wolfgang Langewiesche dated January 2009.I have been around the flying world for along time and this is the first time I have ever listened to the actual recording of an aircraft accident and it turned out to be personally an emotional experience.

These recordings have also been placed on the YouTube web site.

This mid-air collision had seven survivors.  All on board the Embraer Legacy 600, N600XL survived. The number of fatalities was 154.  All 148 passengers and the six crew members on board Gol Transportes Aereos Flight 1907 were killed. No one on the ground was injured or killed.

Both of these aircraft had the latest and greatest collision warning and collision avoidance equipment (TCAS II) installed.  Both of these aircraft were being controlled by a modern air traffic control system using radar for separation purposes.  And both were crewed by professional pilots with extensive flight experience.  

Neither aircraft had strayed off the course cleared to fly by Air Traffic Control. Yet, a mid-air collision actually happened and 154 people are dead.

Why did this collision happen?

Boeing 737-8EH
                                 Photo Credit: Boeing Image

The Brazilian Air Force Accident report on page 258 quoted the contributing factors as:

5.2.1.1.2. N600XL
... lack of an adequate planning of the flight, and insufficient knowledge of the flight plan prepared by the Embraer operator; non-execution of a briefing prior to departure; unintentional change of the transponder setting, failure in prioritizing attention; failure in perceiving that the transponder was not transmitting; delay in recognizing the problem of communication with the air traffic control unit; and non-compliance with the procedures prescribed for communications failure.

b) Air traffic control – a contributor
The authorization to maintain flight level FL370 was given to the crew of the N600XL, as the result of a clearance transmitted in an incorrect manner. 

c) Cockpit coordination – a contributor
The attention of both pilots of the N600XL focused on solving the question relative to the performance of the aircraft for the operation in Manaus, as they had learned of a NOTAM limiting the length of the runway of that airport. This hindered the routine of monitoring the evolution of the flight, because both pilots got busy with the same subject, creating the environment in which the interruption of the Transponder transmission was not perceived.

d) Judgment – a contributor
The pilots judged that they would be able to conduct the flight even with their little adjustment as a crew and with their little knowledge of the aircraft systems, mainly the fuel system and the calculations of the weight and balance. 

The PIC left the cockpit and stayed away 16 minutes, not considering the consequences of overburdening the SIC.

e) Planning – a contributor
The planning of the flight was inadequate. 

f) Oversight – a contributor
The oversight conducted by the operator for the flight proposed was inadequate. The composition of the crew, with two pilots that had never flown together before, to receive, in a foreign country, an airplane in which they had little experience, with air traffic rules different from those with which they were used to operate, favored the lack of a good adjustment between the pilots, along with the already mentioned difficulties of cockpit coordination.

g) Little flight experience in the airplane – Undetermined
The insufficient adaptation of the crew with this type of aircraft and with the DISPLAYS of the respective avionics may have contributed to the unintentional selection of the STANDBY mode and to the subsequent lack of perception of the Transponder/TCAS status.


This accident would not have happened without the multiple contributors cited above. 


 Please see below the pictures of the Radio Management Unit (RMU) and the Primary Flight Display (PFD) installed the the Embraer Legacy for indications of the transponder and TCAS status.


                       
                  Radio Management Unit (RMU)
Transponder Status Indication




Primary Flight Display (PFD) TCAS FAIL Indication

The single item that most would agree to be determined as a primary cause of this accident was the fact the transponder was not operating at the time of the collision.  As a result, the Traffic Alert and Collision Avoidance Systems  (TCAS II) with which both aircraft were equipped was not able to alert either crew of a possible collision.

There are several conspicuous indications of the TCAS/Transponder status in the aircraft instrument panel – eight visible indications in all, with two in the Radio Management Units (RMUs), two in the Primary Flight Displays (PFDs) and another two in the Multi-Function Displays (MFD) (when the MFD was set to display TCAS), and the blinking amber transponder reply light in the “ATC window” boxes on both RMUs.

The Brazilian Crash investigation was unable to discover why it was not turned on even though considerable resources were expended.  A special ergonomics committee was established to see if there was the possibility of a leg or foot movement that could accidentally turn off the transponder.

One positive result of the study discovered not enough consideration had been spent to make the on/off status of the transponder clearly displayed to the crew under all lighting conditions.

The authors of the Brazilian Air Force Accident Report, a 268 page .pdf document failed to emphacize two very important points.  The first one was the failure of either crew to apply the principle of randomness in their aircraft's track.

A brief mention was made to the possibility of a pilot supplied OFFSET being applied to the aircraft track is made on page 14 of the accident report. This is what the report said: Regulate and operationalize the use of OFF SET flight procedures in regions which present communication/radar coverage deficiencies.”

The concept of randomness is recognized today in the form of the Strategic Lateral Offset Procedure (SLOP).  SLOP is in use today and much of the world's airspace, especially the non-radar coverage oceanic airspace as well as in Africa and in China while in radar contact with ATC's approval.

See this Blog's post entitled "Randomness is good!" posted in January of 2010.

They also failed to mention the value of a third cockpit crew member.  Without a doubt, the ideal size of an aircraft's crew is three.  (I recognize I may be beating a "dead horse" when bringing up the subject of minimum cockpit crew size of three.  Today's trend of automating and remotely controlling aircraft is a move to decrease the size of the crew to one and even to completely eliminating the crew.)

If a third crew member had been on board each aircraft, there is increased opportunity for enhanced safety in operations. The richness of the intellectual results of three pilots working together far exceed the results of just two pilots working together.

Since the advent of two man crews in the early seventies, this consideration has been dropped and not ever mentioned in National Transportation Safety Board (NTSB) accident investigation reports. The subject of possible three man crews is a taboo subject.



Cockpit Voice Recorder
I am going to post on this page the actual cockpit voice recorder recordings.  You can access the YouTube web site to listen to them as well. Click here to listen to N600XL and click here to listen to GOL Transportes Aereos Flight 1907.

I would like to suggest you to listen to N600XL recording first to gain a sense of how the operation was being conducted.  It contains approximately two hours and 5 minutes  of the flight.  The sound of the actual collision can be heard at 1 hour and 23 minutes and 45 seconds into the recording.  

The crew of N600XL had not talked to Brasilia Air Traffic Control for almost an hour.  Many attempts to regain contact were made however. There was also no attempt to contact other aircraft for assistance on the air to air frequency of 123.45. 
Please note the pilots of the Legacy only use the word "emergency" in all 10 of their transmissions after the collision had happened.  They did not use the International Civil Aviation Organization (ICAO) phraseology standard word "MAYDAY" in any of them.

The fact the none of the authorities involved mentions or acknowledges the deliberate application of randomness in aircraft tracks is shocking to me. I personally have been applying randomness to my aircraft track for more than 50 years. (Once again, see my post on January 26, 2010 "Randomness is good!")

The application of Strategic Lateral Offset Procedure by either or both crew would have prevented a collision.  The application of randomness in  some form is clearly an option of the pilots-in-command that is rarely talked about or applied but may be the last resort to assuring separation in the event of multiple errors or procedural failures.


The authorities need to take the actions necessary to inform and encourage pilots on the value of randomness.

Do you apply randomness to your aircraft's track? 
If you do not, why?
Should the application of randomness be optional on the part of the pilot-in-command or should it be made mandatory by new regulations?
Your  comments please!

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