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Why was 8.33 kHz spacing implemented above FL195?
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For the past 11 years there has been a regular increase in the demand for operational improvements like resectorisation which, in turn, has led to an increase in the demand for VHF assignments in the band 118-137 MHz. 8.33 kHz channel spacing is the technology that enables this demand to be met.
The frequency planning benefits accruing from 8.33 kHz are driven by the number of 25 to 8.33 kHz conversions that can be achieved. In practice, conversions are limited to sectors having a lower-limit above the mandatory carriage level and which do not use the climax (offset-carrier) system.
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The carriage and operation of 8.33 kHz radio equipment applies to which airspace?
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Since October 1999, the carriage and operation of 8.33 kHz radio equipment applies above FL245 in the ICAO EUR Region. From 15 March 2007, the carriage and operation of 8.33 kHz radio equipment applies above FL195 in the ICAO EUR Region.
Any exemptions – which are expected to be minimal - should be described in State Aeronautical Information Publication (AIP).
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What about non-8.33 kHz equipped State aircraft?
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Non-8.33 kHz equipped State aircraft may fly in the airspace of enforced 8.33 kHz mandatory carriage, provided that they are UHF equipped and the operational situation permits. The flight plan requires the letter “U” in field 10 and the indicator “STS/EXM833” in field 18.
It is important to bear in mind that the handling of non-8.33 kHz equipped State aircraft leads to increases in Air Traffic Control (ATC) workload, and this needs to be taken into account in order to maintain safety levels.
Every effort should be made to equip State aircraft flying above FL195 with 8.33 kHz radios.
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Can I have an exemption?
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If your aircraft is not 8.33 kHz equipped, and the flight is not performed in accordance with published exemptions, FLY BELOW FL195.
A limited number of States may publish exemptions in their Aeronautical Information Publication (AIP). Flights performed in accordance with published exemptions require the indicator “STS/EXM833” in field 18 of the flight plan.
Non-8.33 kHz equipped State aircraft may fly in the airspace of enforced mandatory carriage, provided that they are UHF equipped and the operational situation permits.
Non-8.33 kHz equipped aircraft involved in Search And Rescue (SAR) missions or Hospital (HOSP) Flights are not exempt from the 8.33 kHz mandatory carriage requirements. The flight plan will be processed by the Integrated Initial Flight Plan Processing System (IFPS), but it will be marked by an appropriate text, which can be processed by local air traffic control systems, and which indicates the need for special handling.
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The service ceiling of my aircraft is FL240, but we rarely fly above FL195! Should I fly below FL195 in order to avoid investing in 8.33 kHz radios?
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Equipping with 8.33 kHz radios represents an important investment for aircraft operators. The decision needs to take into account the cost of equipping with 8.33 kHz radios, versus:
- Additional fuel costs when flying at sub-optimal flight profiles;
- A lack of operational flexibility, for example when faced with adverse weather conditions.
It is important to bear in mind that, given anticipated VHF congestion problems, 8.33 kHz channel spacing is expected to be implemented below FL195 in the future. See:
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My radio is 8.33 kHz compliant, but I can’t tune any 8.33 kHz channels?
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Some radio types need to be configured for 8.33 kHz channel operations, for example:
- By using a mechanical toggle switch; or
- By reprogramming via a touch screen display.
When operating in a 25 kHz mode, such radios will not tune 8.33 kHz channels. In a busy cockpit environment, it may be difficult to reconfigure such radios whilst in-flight. Hence, during pre-flight checks, make sure that the radio is configured for 8.33 kHz operations. For example, can the radio display an 8.33 kHz channel, such as 132,055?
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How are 8.33 kHz channels indicated in radiotelephony?
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Amendment 80 to International Civil Aviation Organisation (ICAO) Annex 10, Volume II – Aeronautical Telecommunications – introduces a procedure for VHF communication channels to be indicated in 6 and 4 digits irrespective of whether 25 or 8.33 kHz channel spacing is used.
VHF channels are indicated by:
- Four digits, for channels ending in two zeros – e.g. 118,100 spoken as “ONE ONE EIGHT DECIMAL ONE”;
- Six digits, for all other channels – e.g. 128.075 (25 kHz channel) spoken as “ONE TWO EIGHT DECIMAL ZERO SEVEN FIVE, and 132,085 (8.33 kHz channel) spoken as “ONE THREE TWO DECIMAL ZERO EIGHT FIVE”.
The use of the term “CHANNEL”, previously associated with 8.33 kHz channel spacing, is discontinued.
It is essential that flight crew READBACK the channel number in full, and that controllers verify that the pilot has correctly understood.
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What might happen if you incorrectly tune 132.050 instead of 132.055?
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132.050 represents a 25 kHz channel, whereas 132.055 is an 8.33 kHz channel. Both channels operate on the same centre frequency 132.0500, but the 25 kHz channel has a wider bandwidth. Therefore, the 25 kHz channel may cause unwanted interference on the adjacent 8.33 kHz channels, which are 132.040 and 132.060.
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What happens if you are on a Search And Rescue (SAR) mission or a Hospital (HOSP) Flight and this is shown in Field 18 of your flight plan. You file a requested cruising level anywhere in the Integrated Initial Flight Plan Processing System (IFPS) Zone above FL195 and your aircraft is not equipped with 8.33 kHz capable radios?
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Your flight plan will be processed by the IFPS, but it will be marked by an appropriate text, which can be processed by local air traffic control systems, and which indicates the need for special handling.
Depending on the local arrangements between the air traffic service units along your flight route, appropriate measures will be taken to ensure the safe conduct of your flight, but you must expect to be re-routed outside of the airspace of mandatory carriage.
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What happens if you enter "Y" in Field 10 of your flight plan, but you have no 8.33 kHz capable radios on board, and you file a requested cruising level anywhere in the IFPS Zone above FL195?
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Your flight plan will be processed as usual. However, at some point along your route, you will encounter an ATC sector using an 8.33 kHz channel. The controller will not be able to complete the transfer of your communications to the sector using 8.33 and normally you will be instructed to descend below the lower limit of this sector or be re-routed.
If you still were to enter the sector using an 8.33 kHz channel due to the nature of this channel spacing and the equipment used to communicate on it, you will either not be heard, block out others on adjacent channels, or both and all this in an unpredictable way. Any such misconduct is a serious infringement, a threat to safety and will be dealt with accordingly.
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What happens if you need to conduct emergency radio communication?
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The emergency channel 121.5 MHz is not affected by the 8.33 kHz channel spacing. Its availability and its use remain unchanged.
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Air traffic control issues the request “CONFIRM EIGHT POINT THREE THREE”. How should the pilot respond?
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If the aircraft is equipped with 8.33 kHz radio equipment, the pilot should respond with the phrase “AFFIRM EIGHT POINT THREE THREE”.
If, however, the aircraft is not equipped with 8.33 kHz radio equipment, the pilot should respond with the phrase “NEGATIVE EIGHT POINT THREE THREE”.
To indicate that a certain clearance is given because otherwise a non-exempted aircraft would enter the airspace of mandatory carriage, the air traffic controller should use the phrase “DUE EIGHT POINT THREE THREE REQUIREMENT”.
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I fly regularly above FL195 in Europe, and I have noticed that I still use 25 kHz channels? How come they have not all been converted to 8.33 kHz channels?
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In line with operational requirements and ground infrastructure developments, there will be a gradual increase in the number of 8.33 kHz channels above FL195 in Europe.
It’s not technically possible, however, to implement 8.33 kHz channels in all sectors operating above FL195. The main reasons are that 8.33 kHz channels can only be implemented when:
- The lower-limit of the sector is above FL195 – and many sectors have a lower-limit below FL195 and, thus, use 25 kHz channels;
- The sector does not use climax (offset-carrier) operation, which is currently not compatible with 8.33 kHz.
Therefore, there will inevitably be a mixed environment with both 25 and 8.33 kHz channels.
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