- [Petter] Have you ever heard a saying, "If something can go
wrong, it eventually will?" Well, that was certainly
the case in this story where extraordinary circumstances brought two passenger aircraft
to within meters of each other. Stay tuned. - (indistinct) Mike. Actually I'm--
- 100, 50, 40, 30, 20, 10. - Before I start, did you know
that you can watch this video before anyone else completely ad-free if you have a premium membership
at app.mentourpilot.com? There are also loads
of other perks there so go and check it out. The 21st of October, 2020
was a very windy day in Northern France. An intense low pressure was moving up from the Bay of Biscay
towards the North Sea and it had brought with it
an unusually low jet stream with wind speeds of up to 50 knots at an altitude of only
1,500 feet and above. A jet stream is a narrow band
of extremely strong winds that often travels from west to east over the Northern Hemisphere but normally at a
substantially higher altitude, generally around 30,000 to 35,000 feet. Now, when you have winds traveling that fast at lower altitudes, they will also be hitting mountains, hills, trees and buildings. And at these higher speeds,
that can cause what's known as low-level turbulence. On this day, the pilots who
were going to fly in the region were given significant weather forecasts showing moderate to occasionally
severe low-level turbulence especially around the
Charles de Gaulle Airport area in Paris, France. And at 28,000 feet, en route
towards Charles de Gaulle Airport this morning was
a Hop Airlines ERJ-170. It was being flown on behalf
of Air France with the flight number: Air France 7739 and it had two pilots, two cabin crew and 58 passengers on board. Now, we have no information about the experience
of these pilots but we do know that the first officer was pilot flying and the captain pilot monitoring. As they were getting closer
to their top of descent, the first officer handed over
the controls to the captain and started setting up the
cockpit for the approach. She knew, from the airport's Automatic Terminal Information Service, the ATIS, that she could
expect vectors for an ILS approach into Runway 26 Left
in Charles de Gaulle. The weather she received
from the ATIS indicated a wind of 220 degrees,
26 knots, gusting 31, visibility of 10 kilometers
with clouds, few at 3,300 feet, broken at 4,000 feet, a temperature of 20 degrees Celsius, dew point of 12 and a QNH pressure setting of 1,001 hectopascals. There was also a
significant weather report attached to the ATIS which warned
of moderate to severe turbulence below 1,500 feet, as expected. The first officer knew
that this would mean a quite challenging approach. The wind was reported
as 40 degrees off the runway axis, meaning that in the worst case, she would have to battle crosswinds of around 20 knots in the gusts. When the winds
are gusty which means that they change in intensity, their direction also tends to change, making it even more difficult to handle but a crosswind of 20 knots was well within the
certified crosswind capability of the Embraer 170 so
that shouldn't be an issue. Now, given the report
of severe turbulence together with this crosswind, the first officer decided to add to her normal approach briefing what she would do
in case of a wind shear warning. A windshear is a potentially
dangerous condition where the wind suddenly
changes directional speed and since an aircraft gets its lift from the amount
of air flowing over its wings, a sudden rapid increase
or decrease of the wind can have quite severe consequences. Because of this,
all aircraft manufacturers have stipulated specific procedures
that have to be flown immediately in case of wind shear warning
or if the airspeed and flight path start deviating outside certain criteria even if there is no warning. These criteria are normally
a sudden change of 15 knots of indicated air Speed or 500-feet-per-minute
change of vertical speed, five degrees pitch attitude change or one dot sudden displacement
from the ILS glide slope signal or unusual thrust lever position
for a significant period of time. If any of these indications
are observed, it should be interpreted as the aircraft being in a wind shear. Now, the precise procedure
to follow differ a little bit in detail between different aircraft types but its objective remains the same: keep the aircraft flying
and get away from the wind shear. In case of the ERJ-170, the procedure to follow up for the pilot flying
was very straightforward, push both thrust levers up to max, press the TOGA buttons and follow the flight director
wind shear commands. This would keep the speed
as safe as possible and keep the wings level. Remember that. The procedure also stipulated that no configuration
changes were allowed except lowering the speed brakes if they were used. This was to make sure that
the aircraft didn't suddenly end up in a stall if the flaps were retracted and the speed suddenly disappeared and that the gear would still be out if ground contact became a factor. Now in the case of the pilot monitoring, his role wasn't specifically explained in the Hop wind shear procedure except that he needed to call out
any deviation from the procedure. As the first officer briefed
the captain about the possibility of a wind shear and what they would do if it happened, she also specified that the procedure would have to be continued until
the warning was gone and the aircraft had climbed
to, at least, 1,500 feet as per the Hop procedures. When the first officer was finished with her briefing,
she took back controls. The captain asked air traffic control for descent and they proceeded with completing their descent checklist. At the same time, down on the ground in Charles de Gaulle Airport, a crew from Brussels Airlines were getting their Airbus A320
ready for departure. They were operating
Brussels Airlines Flight 3634 and the four cabin crew members had just finished boarding
their 35 passengers for the short skip over toward Brussels while the two pilots were finishing up the final flight deck preparation. As soon as they were done, they completed their
before-start checklist, requested pushback and start from their stand and started taxiing out for departure from Runway 26 Right, the parallel runway to the
one being used for arrivals. Now, we don't know much about the technical status of the Airbus nor about the experience of the pilots but that will not be relevant
for what's about to happen anyway. But what will be relevant
is the configuration of Charles de Gaulle Airport in itself. The airport has four
almost parallel runways with 27 Right and Left being placed on the
north side of the main aprons and 26 Left and Right
being placed on the south side. On the 21st of October,
the airport was operating in its Southern configuration, meaning that the departing aircraft
were using Runway 26 Right and the arriving aircraft, Runway 26 Left. This type of operation was known as: Simultaneous Movements
on Specialized Runways and was subject to special rules
and regulations to make sure that the approaching
and departing aircraft on the parallel runways didn't
cause any risk to each other. One of those rules specified
that the parallel runways could not be closer to each
other than 850 meters, counted from one center line to the other. In the case of Charles de Gaulle however, this distance was only 384 meters which was less than half
of what was required. This was, of course, not a secret. The airport had been required
to seek dispensation from these rules and were granted this because they could show that they had plans in place for immediate controller intervention in case a go-around would happen at the same time as a departure to make sure that both aircraft
turned away from each other. On top of that, there had also
been studies about the effects of wake turbulence and other factors, enough to convince
the aviation authorities that the parallel operation
although with reduced separation was still safe to conduct. All of this will soon
become super important as we're getting closer
to the actual incident but before I will tell you what happened, I have another important message. Let me share something
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Now back to the video. Now as we're talking
about potential conflicts between aircraft, it's worth discussing the kind of barriers
that we have in force to make sure an airborne
collision can be avoided. First of all, when we're talking
about commercial instrument traffic, we have mandatory
separation between aircraft. This means that, for example,
departing aircraft must wait for a while after the
first aircraft departs until the next one can go
and this can be achieved through either time separation
or by verified radar distances. This kind of separation takes
the speeds of different aircraft into account as well as the
routing and it stays enforced throughout the entire flight, even on routes where there are also additional separations in force
between, for example, aircraft following each other
or crossing each other's paths. On top of this, aircraft
are also separated by altitude with, at least, 1,000 feet
between IFR flights and, normally, even more than that. This is achieved, partially,
by eastbound flights flying on odd flight levels and westbound flights flying on even. Now, there are many more complicated and more specific rules
when it comes to this but, ultimately, it's up to both
the pilots and air traffic control to make sure that proper separation is always maintained. We must all work proactively
and speak up if we think a potential separation problem
might arise and together with the established rules,
this type of mindset has created an extraordinary safe system. But, of course, any system
can fail either by accident or by mistake so if that would happen, there also needed to be
a fail-safe installed and that is: the Traffic Collision
and Avoidance System, TCAS. I will go into the origin
of the TCAS system in a different video but the way
the system works is, essentially, by radio boxes in each aircraft
communicating with each other. These boxes are known as transponders and they transmit their own position, speed and vertical speed
among other things continuously to everyone around. If two of these transponders
feel that they are starting to get close to each other,
they will first alert the pilots to an oral--
- Traffic. Traffic. - [Petter] Which also
brings up a yellow symbol on each aircraft navigation display showing where the concerned traffic is. That alert normally happens about 45 seconds
before a potential conflict and if nothing is done,
this traffic warning then turns into a resolution advisory
when the sensed conflict is about 25 seconds away. That will turn the previously
yellow aircraft symbol red and a red trapezoid will appear on the pilot's primary flight display, showing the pilots how to pitch
in order to avoid a collision. This is also accompanied
by an oral instruction, for example:
- Climb. Climb. - And both aircraft will
receive opposite instructions. Now if a pilot gets a
resolution advisory from TCAS, that will take priority
over any other previously-issued clearance from Air Traffic Control. The pilot flying is supposed
to immediately disconnect the automatics and follow
the TCAS command whilst, of course, still making sure
that the aircraft stays within safe flying parameters. The pilot monitoring have
to monitor the actions of the pilot flying
and as soon as possible, call air traffic control and tell them their call sign and TCAS RA. This is really important
because it will let the air traffic controller know
that the aircraft will be deviating from their clearance and
not to try and intervene as the TCAS maneuvers
of the two involved aircraft will have priority over air traffic control. This will make sure
that there is no collision even if a faulty clearance
have been received or an individual mistake has been made. Now, if ATC would issue
a clearance anyway, the pilot will simply
respond, "Unable, TCAS RA," and keep following
the resolution advisory. This is really important. Once the transponders feel
that a collision is no longer imminent, the resolution advisory will stop
and an oral message saying: - [TCAS] Clear of conflict. - Will be issued. The pilot monitoring will
then call air traffic control advising them that they
are clear of conflict and returning to their
previously cleared altitude. From that point onwards,
the controller can, again, start issuing clearances
and normal operation is resumed and probably some harsh reports written. But one thing to point out here is that TCAS will only
issue vertical instructions, never a turn. About 20 minutes prior
to their expected arrival into Paris, the pilots of Hop Flight 7739
initiated their descent from flight level 280. Given the challenging conditions, they had decided that the approach should be flown with flaps five which would give them
a final approach speed of 142 knots and they
had carefully calculated that the wind was not exceeding their maximum allowed
crosswind component. From my point of view,
the preparation up until this point seems to have been very
professionally handled in every way. They received several
descent clearances and vectors and around time 1017,
they made their final turn towards Runway 36 Left
and captured the ILS localizer. They reported this to
the approach controller who cleared them for approach
and then handed them over to Charles de Gaulle tower
for the landing clearance. As flight 7739 called up the tower and announced that
they were established on the ILS for Runway 26 Left, the Airbus A320 from Brussels Airlines was getting closer
to the holding position for Runway 26 Right. The controller welcomed
Flight 7739 onto the frequency, gave them the latest surface wind of 190 degrees, 22 knots, gusting 32 and then cleared them to land. Now this was more left crosswind than the crew had
initially calculated with but it was still well within
the crosswind limitations. The Brussels Airlines aircraft
had now reached the holding point. They were fully ready for departure so they announced
this to the tower controller who told them to line up and wait, Runway 26 Right. This was read back and the Airbus started slowly moving into
the takeoff position through the howling wind outside. Back in the cockpit of the ERJ-170, the pilots were preparing
for the landing. They configured the aircraft
with gear down and, eventually, flaps five as planned
and at 1,000 feet, the aircraft was fully ready for landing with
all checklist complete. At this point, the first officer
decided to disengage the autopilot. Now it's pretty common
that we disconnect the automatics a bit earlier during
challenging conditions to get more of a feel for the aircraft and get ready for the landing. Handling an aircraft with gusty, almost straight crosswinds
at around 30 knots is quite hard work and it requires a lot
of focus by the pilot flying. The crosswind was coming
from the left in this case, meaning that the nose of the aircraft also would have pointed to the left. In order to keep tracking
down the localizer since the wind was constantly changing,
the first officer would have needed to keep
updating her handling to keep the aircraft flying straight. The constant control inputs
would have been made even harder because of the moderate turbulence that they were also flying through. Now a good way of thinking about how it is to fly
crosswind approaches is trying to picture a boat that is trying to move from one side
of a river to the other, with a stream of water coming,
in this case, from the left. You constantly need to account for and correct for the current
in order to reach that point. As the ERJ passed 500 feet,
the tower controller informed the Airbus on the right parallel runway that the surface wind was now 200 degrees at 21 knots, gusting 36
and then cleared them for takeoff. This was read back
and after a few seconds, the Airbus Pilots pushed
their thrust levers forward and started accelerating
down the runway. At this point, the ERJ was passing its decision height of 200 feet and just as they did,
their indicated air speed dropped from 139 knots to 125
within the scope of only two seconds. The captain called out, "Speed!" And just as he did so, the oral-- - (beeping) Wind shear.
- Warning went off. The captain now
also called, "Wind shear!" Which was confirmed
by the pilot flying who immediately initiated
the wind shear escape maneuver just like they had briefed before. She pushed the thrust levers
fully forward, engaged TOGA and then started following
the wind shear commands on her primary flight display. The aircraft immediately
started climbing away and all of this was done exactly
according to the procedures. But remember how we talked
about how one of the features of the wind shear escape manuever was to keep the wings
of the aircraft level? In a normal go-around,
the pilots would have engaged the lateral navigation mode very early on and that would have guided them to follow the approved
missed approach procedure but that isn't the case in a wind shear. So as the aircraft now kept
its nose straight ahead and started climbing into
an even stronger crosswind from the left, what do you think happened? Just like that boat in the river would do if the stream suddenly
became stronger, it now started drifting to the right, closer and closer to the parallel runway where the Airbus was now departing. And this was further compounded by a slight change
of the heading to the right which happened when
the maneuver was initiated. Eight seconds after the
start of the maneuver, the wind shear warning stopped. The ERJ was at an altitude
of 580 feet, climbing but remember their procedure told them
to continue the maneuver to a minimum of 1,500 feet
even without the warning so that's what they were doing. Three seconds after the warning
had stopped, the pilot monitoring called out that they
were out of wind shear but at almost the same time,
two Master Caution warnings suddenly activated,
indicating a bleed over pressure from both system one and two. This can sometimes happen
when the engine thrust is increased abruptly to max
causing a sudden flow of bleed air from the engines which
can trip the associated valves. But it wasn't a immediately
critical problem at that stage. It would be something
that they could deal with after they go around was completed and because of this, the captain just reset the master caution warning without saying anything further but even though there was
no direct action required, it's likely that this
just further increased the workload in the cockpit
which was already quite high. And it was about to
get much, much worse. As the pilots in the ERJ were executing their wind shear escape maneuver, the pilots of the Brussels Airlines Airbus was blissfully unaware of this. They had just rotated
and were now selecting the gear up and establishing their initial climb pitch which caused the almost
empty Airbus to climb rapidly. Back in the ERJ, things were now
starting to finally calm down a little bit for the pilots. They were passing 1,500 feet, climbing, towards the missed approach altitude of 4,000 feet and since the wind shear was now gone, the captain
called up the controller and informed them that they had gone around straight ahead
to 4,000 feet due to wind shear. When the controller heard this,
he replied that he would call them right back. He had seen that the ERJ
went around but that, in itself, didn't worry him since he assumed that the missed approach
procedure was being followed. He had no idea about
the wind shear at this point and how that was affecting
the way that the pilots were flying their missed approach. Instead he was now trying
to coordinate with Le Bourget Tower which was controlling
the adjacent airspace to allow the ERJ
to make a left-hand turn. He normally had direct contact
with Le Bourget via intercom but this wasn't working
for some reason so he now had to call
them on the phone instead. That meant a further
five to 10 seconds delay without any turn instruction
from the tower and meanwhile, the ERJ kept drifting
steadily to the right. In the cockpit, the ERJ crew
had now engaged heading select at their present heading of 259 degrees. They had also started pitching
down slightly to accelerate, retract flaps and the landing gear in accordance with their procedures. Apart from that, they were standing by for further ATC guidance,
again all very professionally done. But, of course, what they didn't know was that below them,
they now had a very light Airbus A320 climbing fast towards them. At time 10:22:14 seconds,
that's 45 seconds after the initiation of
the wind shear maneuver, an oral, "Traffic, traffic," warning was issued inside both the ERJ
and the A320 cockpits. At the same time,
the tower controller called the ERJ crew and asked them to make an immediate turn
to a heading 240 degrees. The use of the term, "Immediate"
is emergency phraseology reserved for serious events where action needs to happen right away. The ERJ Captain responded,
read back the new heading, entered it in the Mode Control Panel and the aircraft started turning. As he did so, a short-term conflict, an STCA, was issued
inside of the tower, indicating that the two aircraft were now getting way
too close to each other. One second later, as the ERJ
climbed through 2,150 feet, a TCAS resolution advisory
was issued, instructing the crew to, "Climb, climb." The pilot flying, again,
reacted immediately and pushed the thrust levers
forward to the TOGA detent and started following
their resolution guidance but this also meant that she stopped her turn on a heading of 250 degrees. This meant that the left turn
they had received for separation was now not being followed. At the same time, the transponder
in the climbing Airbus below also issued their resolution advisory; in their case, "Level off! Level off!" Which the pilots immediately
complied with and managed to stop their climb at around 2,000 feet. As the pilots were complying
with the TCAS RA, the controller desperately called the Airbus crew asking them to, "Stop climb altitude, uh, stop climb the
present altitude, please!" But to that the Airbus crew
just responded, "TCAS RA," which was the correct thing to do. Now if you're wondering why
the controller sounded nervous here, it was because from his vantage point, he saw that the ERJ-170
was not turning as he had asked them to do. And he could also see
how the Airbus was still climbing and it
didn't look like they were actually leveling off. When he then looked down
onto his radar screen, the two aircraft radar echoes combined and could not be
distinguished from each other which must be a terrible feeling. The controller later explained that it made him feel very powerless. The ERJ captain now called up and said, "We have also had a TCAS RA." And to be perfectly honest,
in this whole mess, the only real mistake made
by any of the pilots was to not advise the controller
of the ongoing TCAS RA as soon as they received it. Since the Airbus had now stopped climbing and the ERJ was
still climbing away, the, "Clear of conflict," message
was now issued in both cockpits and even though they
didn't formally advise the controller of this fact,
the ERJ crew accepted a further left turn
to heading 200 degrees. The controller then again told
the Airbus crew to stop climbing, to which they, this time,
responded, "Affirm," as it was in line with
the previous TCAS instruction and a few seconds later,
they were cleared to turn right onto a
heading of 360 degrees and continue their climb. They then continued their flight
without any further incident whilst the ERJ-170 executed
a second approach and landed uneventfully. At the closest point,
the two aircraft had been 0.09 nautical miles away
from each other laterally. That's 166 meters and only
460 feet or 150 meters vertically. That's very close when you're traveling at around 90 meters per second. But the system did work. The last Safeguard kept
a potential disaster from happening just as
it was designed to do. The task for the investigators, of course, now became to figure out
why this had happened in the first place. The crew of the ERJ-170 were interviewed and the investigators could
relatively quickly establish that they had, with the exception
of the incorrect TCAS phraseology, done a great job under the circumstances. The same went for the pilots
in the Airbus as well as the controller. Everyone had done, within reason, what they were expected to do. So this naturally turned
the investigators' attention to the design on the airport
and the exception it had received to operate parallel operations with the two runways
that close to each other. It was quickly found that rules
regulating simultaneous departures from parallel runways had provisions for abandoning this type of operation if the crosswind condition
exceeded 25 knots but that was not the case with simultaneous
approaches and departures. This, and the fact that
a go-around in a wind shear where the pilot cannot
follow neither ATC commands nor missed approach procedure had not been taken into account in the studies that led
to the exception soon became very clear. It was also found that
three similar incidents had already happened
which two of them had taken place at
Charles de Gaulle Airport. The recommendations
from the final report therefore was for the French aviation authorities to reassess the suitability
of this type of operation at Charles de Gaulle
based on the obvious risk of wind shear escape maneuvers. It also suggested that ICAO
consider implementing rules for when these type of parallel operations would be allowed during
special weather conditions like wind shear, turbulence
or thunderstorms. Now for us pilots,
the report simply highlighted how important proper phraseology can be in situations like this in order to keep everyone in the loop. It also showed how important
the job of the pilot monitoring is in checking the overall situation of the aircraft and maintaining
situational awareness about what's happening around you. If the weather is very
marginal like it was in this case, it might be a good idea
to tell the ATC controller when you're on the approach
that there's a high likelihood of a go-around. That could help the controller to check for potential threats early and to give them
a better mental preparation in case of a go-around actually happening. The Hop operations manual
was updated to say that the wind shear escape maneuver
was completed when the aircraft was out of the wind shear
and with sufficient terrain clearance, not just at 1,500 feet. Now I found this to
be a fascinating story with a lot of complex components and a great example
of how the aviation world uses incidents to keep
becoming better and safer. If you want to see more videos like this, well then check out these
and consider becoming a member of my wonderful Patreon crew. That will help me to continue
to produce these type of videos. There are links to both my Patreons,
my merch, apps and my sponsor in the description below so go down and check them out. Have an absolutely fantastic day and I'll see you next time, bye-bye.
