Flight prefixes

Why does FlightAware continue to use CALLSIGN prefixes with FLIGHT NUMBER numerals ? In most cases these are different. The three-character ICAO prefix , such as RYR , EZY , etc.refers to callsigns. Occasionally the numerical string which follows this prefix can also be the flight number , but this is by no means always the case. To work with flight numbers , the IATA prefix should be used , so RYR should be FR , and EZY should be U2 , and so forth for all carriers.

I am not an advocate of the local site, but its user.
The issue is easy without the refrence to misundesrtanding between 2 participants of air traffic.

You refer to the 3-character call sign prefix, which is used in the internatinal air transportation, where the operators and operating agencies have to follow article 77 of Convention and the annexes to the Convention.
The web site and majority of its users are located in the States

The US F.A.A. give the following explanations of the use of the call signs for the operators:-
“The three types of call sign designators and telephonies authorized for use by FAA ATO
and described in this advisory circular are as follows:
a. International Civil Aviation Organization (ICAO) three-letter designator (3LD) and
associated telephony …;
b. U.S. special call sign designator and associated telephony …; and
c. Local call sign designator and associated telephony …”

The U.S. F.A.A. rules of the allocation of the call signs between the operators (operating agencies) do not contradict with ICAO rules, which allow the use of non ICAO abbreviations during the tranmission between two points of the air traffic (expl, para of Annex 10 to the Convention on International Civil Aviation).
It means, 2 participants of the same air trafic shall undesrtand each other smothly and on 100%, irrespective to the exessive formalities, during their duty on the route.

Expl, QTR738 and QR738 and QatarAirways738 and Qatar738 has non contradictory equal meaning for all participants in the zone of the air trafic.

The majority of our data sources are ICAO-oriented, not IATA-oriented.

IATA prefixes are less unique than ICAO prefixes.

There are many aircraft that operate without an IATA flight number.

We handle CSD (CSS) internally and generally both the flight number and the disambiguated callsign suffix can be used interchangeable.

The flight search UI will automatically translate IATA prefixes to ICAO prefixes for you, where possible.