Dec 26
Merry X-mas!
From CrossingTheSkies staff, we wish you a nice and merry christmas, and a happy new year also! We hope you found this blog beautiful, and we thank you all for visiting it!
We expect a new year (2009) with plenty of new and fresh material, new posts, aviation news, aeronautics and some more.
See you around!
Andrew && Angel
Author: La Roche Spotters
Dec 15
Cross-polar routes
Since 2001, when Russia opened their airspace borders, some airlines thought that flying across the north pole would be much faster, like a shortcut. As a matter of fact, they got right. You can almost save up to 4 hours of flight, flying through the north pole instead of the regular routes.
These regular routes are the PACOTS (Pacific Organized Track System) going from the U.S. west coast to Japan and Honolulu. These are a set of predefined routes (it works like NAT routes), that start within US airspace (a fix) and they finish within Japan airspace (another fix). Between them, there’s just some waypoints defined with coordinates (there are no navaids to define them). So, an airplane departing from JFK had to go to the west coast and then, get en-route in these tracks.
United Airlines, Continental and other Japanese airlines started operating routes through the north pole. Then, they would save time, fuel and consequently money. But it’s not that easy. We all know that in the north pole it’s kinda cold, so it’s pretty likely that kerosene solidify. Nevertheless you can also descend to a lower altitude and modify your original route.
In addition, because of the earth’s magnetic field shape, the cosmic rays are much intense in that area. Therefore, the radiation exposure seems to be greater than the normal quantity. Some expert says that the total radiation exposure up there could be equal to 3 X-ray taken. Here you can appreciate a cross-polar route from JFK to Beijing (Japan) at Great Circle Mapper.
ATC services are not available, since we have no radar coverage. To sum up, it’s really an amazing adventure flying this kind of routes. Pilots must have good skills, and a big coat!
Dec 9
Designing an airport runway
One of the key elements of an airport is the runway. In fact, if there is no runway, there is no airport anyway. The runway is the place where airplanes take off or touch down. Then, the runway features will be an important issue to bear in mind.
First of all we have the runway orientation. The runway direction will be a major fact in terms of airport operations. A wind intensity and direction research must be done in order to obtain and gather wind data, and then determine the most likely wind direction in that area. Now let’s talk about physical characteristics.
The two more important sizes are the runway length and the width. Depending on the aircraft expected to operate on that airport, you might use larger or shorter distances. There is no specific runway length established by FAA or ICAO, but could change from 200 meters to infinite (if we could have that region). About the runway width it is mandatory to be greater than 18 meters up to 60 meters (able to land an A380). There are other physical matters, like strips up to 150 meters (around the runway) and shoulders up to 15 meters (paved margins at both sides of the runway).
In addition, to promote the most rapid drainage of the water, there should be a transverse slope not greater than 2%. Longitudinal slopes cannot be greater than 2% (just imagine a 3000 meters runway, 2% would mean 60 meters of vertical variation).
Dec 4
Fly-by-wire and Airbus Laws
Nowadays, commercial airplanes do not fly with metal wires moving the ailerons anymore. Now it is managed digitally, from the source (the sidestick or yoke movements) to the control surfaces movement. This system is called Fly-by-wire.
The fly-by-wire system consists of some computers (5 computers on board the Airbus’ planes, 3 primary and 2 secondary), that read the pilot movements, interpret them, and it sends a modified signal (from the original one) to the control surfaces.
All these means that the airplane movements will not match proportionally what the pilot is doing actually. This philosophy shocked a lot of pilots, they couldn’t imagine flying something without a cable between the yoke and the surfaces. Finally, it was demonstrated that this system was much efficient, safer and much versatile.
Airbus was the first one using fully fly-by-wire (A320 were the first) and they create a set of laws that would govern this system. There are 4 laws: normal law, alternate law, direct law and mechanical back-up depending on the degradation of the airplane.
- Normal Law: It is on when normal operation is carried out. It controls the 3 axis (pitch, roll and yaw) balancing the aircraft and interpreting the sidestick movements. In addition, it offers some envelope flight protections (on pitch attitude and roll attitude) and alleviate load factors, like the gravity when turning for a much better comfort.
- Alternate Law: If a minor failure exists (sensors disagreement, computer blackout, hydraulic system upset,etc) this law becomes the active one. Basically it provides the same control as the normal law, but without protections. Also, the roll control becomes “direct law-like” control.
- Direct Law: If a major failure exists (radio altimeter failure when approaching, 3 inertial references down, etc) this law become the active one. Then, the movements of the control surfaces are the same as the sidestick movements. There is no auto trim, and any protection system will be available (even alpha-floor for stall warning).
- Mechanical Back-up: This mechanical aid should be used when the electrical system is all down. Then, the airplane can only be controlled with the trim wheel for pitching, and rudder pedals for rolling.
Dec 1
The freedoms of the air
The freedoms of the air are a set of rights signed between countries, which grants the right to overfly an airspace and/or to land in those countries (bilateral treaties). There are 9 different freedoms, depending on the kind of flight. All these rules were defined in 1944 during the International Civil Aviation Convention in Chicago.
The right or privilege, in respect of scheduled international air services,…
1st.- …granted by one State to another State or States to fly across its territory without landing.
2nd.- …granted by one State to another State or States to land in its territory for non-traffic purposes
3rd.- …granted by one State to another State to put down, in the territory of the first State, traffic coming from the home State of the carrier
4th.- …granted by one State to another State to take on, in the territory of the first State, traffic destined for the home State of the carrier
5th.- …granted by one State to another State to put down and to take on, in the territory of the first State, traffic coming from or destined to a third State
6th.- …via the home State of the carrier, traffic moving between two other States
7th.- …granted by one State to another State, of transporting traffic between the territory of the granting State and any third State with no requirement to include on such operation any point in the territory of the recipient State
8th.- …of transporting cabotage traffic between two points in the territory of the granting State on a service which originates or terminates in the home country of the foreign carrier or (in connection with the so-called Seventh Freedom of the Air) outside the territory of the granting State (consecutive cabotage)
9th.- …of transporting cabotage traffic of the granting State on a service performed entirely within the territory of the granting State (stand alone cabotage)
Freedoms of the air
Nov 27
The SELCAL Code
The SELCAL system or Selective Calling system, commonly used in aeronautical communications, is a multiple system that allows the radio ground-based operator to send a signal to the aircraft that wants to establish a communication. In other words, when an ATC want to talk with an airplane flying over the ocean, he pushes a button and the airplane’s crew receive a message. That is kind of worthy in oceanic routes, where HF (High Frequency) communications give a lot of background noise, and pilots usually turn off the squelch until they receive this signal.
In order to identify each single aircraft, a SELCAL code is assigned to each one. This code is made by 2 pairs of letters (using from “A” to “S” excluding “I” and “O”) and each letter has an assigned frequency. Then, when the operator wants to talk with that aircraft, a 4-tone signal is sent with those letters. Everybody who is in that frequency will hear that sound, but only the one with that code will receive a sound alert (bling-blong-like sound) and a light alert.
There are 10920 different SELCAL codes. That’s the reason why there are duplicate codes (two airplanes, same code). Only airplanes operating oceanic routes use that system though. So, when a duplicate code exists, they make certain that those airplanes will operate in widely separate parts of the world.
ARINC (Aeronautical Radio Inc.) issues these codes in the US. You can find real-world SELCAL codes in this website just entering the registration number.
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