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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ETOPS: Unlimited Trustworthiness
The ETOPS (Extended-range Twin-engine Operational Performance Standards) defines the twin-engine aircrafts requirements to operate flights where the nearest enroute alternative airfield is further than 60 minutes.
At the beginning of commercial aviation, because of the lack of regulations concerning alternative airfields further than 60 minutes, the air carriers started putting pressure on Aviation Administrations to be modified, in order to be able to operate transatlantic routes with twin-engine. Because of that, ICAO and the FAA drawn up a new reguation that allowed to operate those routes.
Nowadays, there are several ETOPS ratings depending on some parameters. These parameters are including the engines and systems’ reliability, crew training and ratings, manteinance and so on.
Author Andrés Meneses
These are the different ETOPS ratings issued these days by Aeronautical Authorities:
- ETOPS-75
- ETOPS-90
- ETOPS-120/138 (138 minuts is a 15% plus 120 minuts, in order to cover a little part of the Atlantic Ocean, not covered with ETOPS-120)
- ETOPS-180/207
An ETOPS rating is gradual. That means if you want to reach ETOPS-120 rating, first of all the aircraft must have reached the ETOPS-75 rating (with 200 sectors with 98% relieability), then the ETOPS-90 rating (with 300 sectors with 98% reliability), and finally the ETOPS-120. For example, in order to achieve ETOPS-120 rating, the airplane must prove less than 0.05 per mil in-flight shut-down. That means, flying 20.000 flights there’s only one in-flight shut-down (obviously, an airplane does not achieve 20.000 routes in its life).
There’s a tremendous application called Great Circle Mapper where you can compute each ETOPS rating maximum range around the earth.