I'm working a crazy schedule this month. Crazy awesome, that is. For the first time in my five plus years at the airline, I'm working three days followed by four days off. It's crazy having four days off in a row every week. It hasn't exactly been as much of a boost to my homework productivity but it has been a boost to my Netflix queue. Currently, I'm avoiding homework to write about something that happened on a flight last week.
"When something does happen that accellerates the pulse we usually have the ability to problem solve or otherwise mitigate said accelleration."
I've recently crossed the 5,000 hours logged threshold and I'm getting pretty comfortable in my "new" airplane that I transitioned to in 2013. I've got about 1,200 hours in the jet and there aren't a lot of things happening for the first time anymore. Rigamoral and boring is the ideal as a pilot. We strive to limit the exciting or abnormal happenings. When something does happen that accellerates the pulse we usually have the ability to problem solve or otherwise mitigate said accelleration.
Recently on our return flight to Chicago from El Paso, we were in search of a smooth ride at 31,000 feet. Our dispatcher had filed us down low in an effort to avoid the turbulent air above, however, we were bouncing along the cloud tops right at 31,000 feet. I try to reiterate to the passengers whenever we're in turbulence that it's nothing more than an annoying inconvenience, but we still try our best to avoid it. So up we went, 33,000, and eventually 35,000 feet. Even all the way up there we were still grazing the upper reaches of the clouds.
We had only been in flight for about 30 minutes by the time we made it up to 35,000 feet and the ride was finally starting to smooth out as we progressed towards Chicago. As you can imagine, the airspace up at these altitudes is usually pretty busy with airline and business jet traffic. Today was a little less busy as it was mid-day on Sunday, but we still had a decent amount of airplanes crossing our path. When another airplane crosses in front of us, air traffic control will alert us so we can be aware of them. They'll tell us which direction from us they are, which direction they're travelling, and their altitude and aircraft type. This helps us locate them, and ensure they're where they should be and that no collision threat exists.
"Traffic at your 2 to 3 O'clock, north-west bound, leveling a thousand feet below you, is a Phenom."
"Traffic at your 2 to 3 O'clock, north-west bound, leveling a thousand feet below you, is a Phenom." An Embraer Phenom is a very light jet that some private operators fly as well as some corporate and charter companies. This call from ATC was nothing out of the ordinary, we get these types of alerts from ATC probably a hundred times a day. We look outside for the airplane, make sure we're going to miss them, and then we resume reading the instruments (newspaper).
It's also not uncommon for a climbing aircraft to trigger a traffic alert from our anti-collision system called TCAS (Traffic Collision Avoidance System). This alert sounds an aural caution "TRAFFIC! TRAFFIC!" to let the pilot know that an aircraft is approaching and could become a collision threat. At lower altitudes these alerts are very common and almost always never become a resolution advisory (actual collision threat exists). At higher altitude however, these alerts are almost non-existent. Not today.
As the aircraft approached their cleared altitude of 1,000 feet below us, we recieved the "TRAFFIC! TRAFFIC!" alert. Up at 35,000 feet this is acutally pretty rare because climb rates are usually reduced in reduced vertical seperation airspace (RVSM). This alert got our attention and started that accelleration we try to avoid. The TCAS system is designed to alert us of traffic visually, aurally, and if needed, also provide vertical escape guidance both aurally and visually. It's a tiered system that escalates the alerts as needed based on the threat of collision. The system had shown us this aircraft visually at first, as just another airplane near us. Next it will show you an airplane that has a potential for a collision by changing the color and symbol on our display and giving the first aural alert of "TRAFFIC! TRAFFIC!" Finally, when an actual collision threat exists the display changes again to a red symbol and the aural alerts now give commands on what manuever to begin in order to avoid the collision.
"As a testament to the limitations of the human body during times of stress, I never heard the first aural RA."
"CLIMB! CLIMB NOW!" was the resolution advisory we received. The display also modifies our vertical speed indicator to show what rate of climb or descent is required to vertically navigate away from the threat. This was actually a corrective resolution advisory as the first one told us to descend. As a testament to the limitations of the human body during times of stress, I never heard the first aural RA. I think it was "MONITOR VERTICAL SPEED" – even though the aircraft was in level flight, we were experiencing some light mountain wave turbulence which causes the aircraft to oscillate a few hundred feet. Our vertical speed indicator is an instananeous indicator and will sometimes show a climb or descent as much as 1,000 feet per minute for brief moments. This tricked the TCAS into thinking we were in a descent when the RA was triggered.
"The tricky thing here is getting the aircraft away from the threat expeditiously while simultaneously avoiding loading the wing too much and inducing a high altitude stall. Yay we missed them! Boo now we're falling with style!"
After initially commanding us to maintain a rate of descent to avoid the aircraft, the system calculated that our descent was no longer an option to avoid the aircraft and it then commanded us to climb. The tricky thing here is getting the aircraft away from the threat expeditiously while simultaneously avoiding loading the wing too much and inducing a high altitude stall. Yay we missed them! Boo now we're falling with style! Up at this altitude the airplane has a much smaller margin of "too fast" and "too slow," it is inbetween these speeds that we must remain in order to be considered still flying. Entering a high rate of climb at this altitude is usually non-sustainable (and non-habit forming). Our goal in this situation was to climb fast enough to avoid the conflict, but not so fast or too quickly to deplete the energy on the wing to induce a high altitude stall.
Luckily for me and for all the people behind me, we managed to avoid all the pitfalls of the event and complete an uneventful flight. It did take a few minutes for the reality of the situation to register. We spent quite a few moments recollecting what happened and why. It's very rare for this type of event to happen, especially at such a high altitude where aircraft are meticulously seperated from each other.
We never heard the other aircraft on our frequency, so it's likely he had already been switch to a new controller. We don't know if they had the wrong altitude programmed or if they were simply climbing so fast the computer calculated a collision risk. What a lot of people don't know is that scenarios like this one is how our modern day FAA got started.