One of life's occasional frustrations is when BA - or any airline - cancels your flight, or there is a long delay on it. This thread is to help you find out the reason, and indeed feel free to ask questions below about what happened to your BA flight. In some cases it's useful to find out to support a claim for EC261 / UK261 compensation, where "extraordinary circumstances" is a reason why you may be out of socpe for compensation. See the main EC261 thread via the BA Forum Dashboard for EC261 / UK261 specific issues.

See also this thread.
https://www.flyertalk.com/forum/brit...need-know.html

Delays - how to find out the cause
1) Listen to the flight deck's announcement just as doors are closing after boarding. On every delayed BA flights that I've been on, the flight deck gives a full description of why there is a delay. It may be worth making a note of what is said, this is by far the best and most accurate report you are going to get. I appreciate that sometimes it's difficult to hear what is being said, but on longhaul you can plug in you earphones to the inflight entertainment system to hear more clearly.
2) Expertflyer - there is a dispatch code put into Amadeus by ground staff with a 2 letter code giving a broad reason code (see codes below). This is found in Desktop Verion / Flight Status / Search by Flight (the default search). Note this information is only visible for around 48 hours. If you don't have access to Expertflyer then by all means ask below.
3) Flightradar24 - in this website you can enter your flight number and you may be able to identify your aircraft registration (e.g. G-TTNF). By clicking on that registration, or entering it into Search, you can see the previous history of the aircraft and see where delays happened.
4) Twitter - sometimes a search will find out more information if someone else has complained about the delay/

Cancellations
These are more difficult to work out, since if done in advance all you will get from BA is some sort of notification of disruption and often a menu that allows you to choose new flights. In this you will not find clarity on what happened to your original flight - and contact centre staff may not know either. And sometimes, to be brutal, BA doesn't particuarly want to go out of its way to say (e.g.) we do not have enough crew members to run this particular service. Expertflyer (see above) used to give information about this, but for the last few months this hasn't generally been visible - I don't know whether that's on the BA side or Expertflyer or a bit of both. All EF shows is that the flight is cancelled. You may alternatively get some clues from Flightradar24, particularly if your route needs a particular aircraft type and the designated aircraft is stuck somewhere else.

Both cancellations and delays
5) Don't forget to scan down the BA forum for a page or two, you may see an existing thread with a lot of information, particularly if something like weather or a computer failure was at fault.
6) Ask at the airport. Agents can look up information for you and a polite request should be met with a useful reply.

Amadeus dispatch codes - main ones
ZO - Operational - a bit of a catch-all this but it could include late arriving crew. Very often ok for EC261.
ZW - Weather - delays caused by poor weather - generally out of scope for EC261.
ZY - Rotational - a delay caused by a previous delay to services and the aircraft is in catch up mode. Often, but not always, ok for EC261.

Less frequent codes
ZA - ATC
ZC - Cargo
ZD - Security delays
ZE - Engineering
ZF - Flight crew (though usually ZO is used)
ZJ - IT delays (also EO is used here)
ZK - Cabin crew (again more likely ZO is used)
ZL - Ground fleet
ZM - Catering
ZP - Passenger services
ZR - Ramp / apron
ZT - Control (load sheets for example)
ZZ - Authorities / government action

Three and four letter codes
OPE - Operational (all sorts of issues get given this, but crew held up in security would be one example of thousands)
WEA - Weather
ARP - Airport (this can mean weather related restrictions)
FCR - Flight Crew
CCR - Cabin Crew
COM - Commercial (COMN usually means a flight BA cancelled some time ago, typically over 2 weeks, so avoiding EC261 compensation)
IND and INR - Industrial / strikes
ITS - IT system failure
HLD and HDL - ground handing
ROT - Rotational (delay due to delay on previous flight)
TEC and TCH - Technical problems on the aircraft
DAM - Damage (e.g. lightning strike)
Note this usally comes over as 4 letters, so OPEY means operational and potentially yes to EC261. WEAN - means bad weather and no EC261, at least from the airline's perspective
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Just to reiterate - by all means ask here for more help and assistance for why your flight is late after going through the above, but for EC261 specific enquiries there is a thread for those queries and it's best to put them in that thread rather than spreading information all over the forum.