Ok, joking aside, we can answer this question with data from the US Bureau of Transportation Statistics. I see you're in England, but you say anywhere in the world and I live in the US and this is the only data I'm aware of, so it's the data I'm going to base my answer from.

I'm home now with a stable Internet connection so I can download the large export of their database for delays reported in November 2023 (the latest month with data).

https://www.transtats.bts.gov/ot_del...elaycause1.asp
https://www.transtats.bts.gov/DL_Sel...6_anzr=b0-gvzr
https://www.transtats.bts.gov/Tables...6_anzr=b0-gvzr

I'm using the Marketing Carrier database, not the Reporting Carrier database so that regional flights operated by Mesa, PSA, Envoy Air, etc show up as the mainline carrier, Delta, American, United, etc since I'm guessing the teacher won't recognize US regional airlines.

Not sure if the teacher is into the minutia, but I'm looking at arrival delays, not departure delays. A plane could leave late and still arrive on-time or early, but most people only care about whether they arrive late.

With all the details out of the way, the most delayed flight in Nov 2023 was a flight from Amarillo, TX (AMA) to Dallas / Fort Worth, Texas (DFW) on AA on Nov 14, 2023. Unfortunately the government doesn't provide flight numbers. The flight was delayed 3502 minutes or 58.36 hours! Yikes! Cause of the delay was Carrier Delay (so likely some maintenance issue or something). Aircraft was N834AW, an American mainline A319.

Found the flight on FlightAware. It was AA483.
https://www.flightaware.com/live/fli...010Z/KAMA/KDFW



To answer the actual question, flights that commonly have delays I removed all the flights that had a delay less than 60 minutes and ended up with a list of delays from 315 originating airports and 313 destination airports.

With 50 delays, FLL to ATL tops the list!

Here's the top 12 (a few airports were tied for 37, so I'm listing 12 instead of 10) -
FLL-ATL - 50 delays
LAS-LAX - 49 delays
MCO-PHL - 45 delays
MCO-EWR - 44 delays
LAX-LAS - 41 delays
ATL-FLL - 40 delays
MCO-ATL - 39 delays
PHL-MCO - 38 delays
SAN-LAS - 38 delays
ORD-LGA - 37 delays
EWR-MCO - 37 delays
PHL-CLT - 37 delays


Raw Data - https://docs.google.com/spreadsheets...rue&output=csv

Pivot Table - https://docs.google.com/spreadsheets...35&single=true
* Origin Airport on the Left, Destination Airport across the Top, so Cell B2 is DFW-ABE, 0 delays and Cell C2 is DFW-ABI, 7 delays.

EDIT

Digging into the data a little more, there were 50 delays on flights from FLL to ATL. Those delays were caused for the following reasons (some flights may be delayed for multiple reasons) -
Carrier Delay - 40
Weather Delay - 2
National Air System Delay (NAS) Delay - 31
Security Delay - 1
Late Arriving Aircraft - 36


More interesting, I was able to find flight numbers in the data. The flights with the largest number of delays in America in Nov 2023 -
AS66 - 19 Delays
OO5039 - 14 Delays
B6914 - 13 Delays
AS64 - 13 Delays
OO3735 - 13 Delays
OO4232 - 13 Delays
AS70 - 12 Delays
AS65 - 12 Delays
NK5 - 12 Delays
OO3116 - 12 Delays
MQ3779 - 12 Delays
B62465 - 11 Delays
B62466 - 11 Delays
NK981 - 11 Delays
NK299 - 11 Delays
NK1608 - 11 Delays
B6568 - 11 Delays
OO3068 - 11 Delays
NK298 - 10 Delays
NK226 - 10 Delays

The results are pretty fascinating! They don't match up with the airport list further up in the report. The first flight is in Alaska, the second one is a regional flight in Colorado, and finally the third is a flight up the East Coast from FLL to Westchester in New York. I made that joke about Frontier and JetBlue, but these results make Alaska, JetBlue, SkyWest and Spirit look bad!

Data -
https://docs.google.com/spreadsheets...21&single=true