Connections in LHR terminal 5
 

I am flying business class, midweek in June, into LHR from NY/JFK on flight BA0174 landing at 6:55 am and then connecting to BA0346 to Nice at 9:15 am. The scheduled layover is 2 hours and 20 minutes. All luggage is checked thru

1. Since this is a busy time of day, how long should it realistically take me to get thru security, etc?
2. Since both flights are in terminal 5, will I be able to spend any time in the BA business class lounge?
3 Are the lounges close enough to relax to be able to board in time?
4 Will I be able to use fast track for security or are the E gates a better choice?

You should expect to be in the departure area after security around 30 minutes after leaving the aircraft.
Yes, you should get about an hour in the lounge ( 2 hour 15 min connection, 30 minute transit, leave the lounge 30 to 40 mins before departure to get to the gate at least 20 mins before departure)
Yes, its likely your nice flight will leave from an A gate. There are 2 business lounges in the A gate area, onecatcthe north end, one at the south end. It will be about a 5 minute walk from the lounge to tha gate.

In the unlikely event its a B or C gate then its 10 to 15 minutes-ish to the gates from the A lounges, or use the lounge in B.

the flyertalk t5 connection guide :

https://www.flyertalk.com/forum/brit...ispreloading=1

Last thought…. Will I be able to use fast track for security or are the E gates a better choice?

Why enter the UK when you don't have to?

Keep it simple and stay within the connections routing.

So no fast track going thru security in T5?

There is a fast track transit security, its not always open and you won't know if its open or how busy it is until you are well into the transit process.

i too would just use the transit route unless i find a huge q to enter the transit area. Normally i do not see a lot of difference between the 2 routes.

The last few times i have gone through transit security i have sailed through. My 30 minute estimate to get from plane into departures includes about 10 minutes for security, just in case. If things line up well on the day its 15 minutes from leaving the plane to departure area, so 30 minutes from touchdown

e-gates are for immigration to enter the UK. Unlike an international to international transit in the USA, you don't need to enter the UK (but can if you really want to).

Security is a separate process

Thanks for your detailed response! Very helpful