Some reasons why flight delays may happen

Although most flights tend to be on time, flight delays are just as horrible as they are inevitable. There are several reasons as to why( flights to Lahore from UK, say) are delayed:-

1. Boarding delays. Sometimes it takes too long to get passengers boarded.
2. Engineering issues. If problems are detected during pre-flight checks, there may be delays whilst they’re fixed.
3. Delay of other flights. If one flight (say, flights to Karachi from UK) is delayed, the connecting flights are also delayed. Same goes for airframe scheduling issues & congestion in air traffic.
4. Weather-related issues. Weather, flooding and other natural-origin causes can lead to planes unable to fly, or not being available on time.
5. Security measures:- If there is a potential for bodily harm, or there is a national or international security issue; air traffic control and the flight authority in the country you’re in can cancel or delay flights to Islamabad from UK (say).
6. Crew problems:- The crew must be scheduled - if there’s a strike, a walkout, traffic problems, storms, or any other reason the crew doesn’t show up, they must find a new crew.
7. Go-Arounds: A go-around occurs when an aircraft is just about to land at an airport and the pilot decides it’s not safe to land. So you will see/feel the plane suddenly increasing altitude, as if it were taking off again. Of course, this affects the arrival time for that flight; as it could take up to 30 minutes for the aircraft to return and land again.
8. All of which lead to a problem: missed take-off slots. It means that the plane’s (flights to Sialkot from UK, say) take-off could be further delayed for anywhere from typically half an hour to much worse.

Airlines allow for a little bit of flexibility, and it’s important for passengers to understand such so they can fit some flexibility into their schedule, too.

Source: https://cheapflightstodetroit.blogspot.com/2023/01/some-reasons-why-flight-delays-may.html