Everything around there starts about 5 am. The trains start their day from their maintenance base at Northfields, a few stops east, so the first ones run west from there to Heathrow, round the loop or out to T5, and then start back towards London.

There's only one significant way in from the terminal to the T4 station, there are ticket gates (and baggage restrictors) across the entrance, so get friend to wait there. There's also an Underground official at the gates if either of you feel like chatting. Because the trains wait at T4 for several minutes you can get off, say Hi to friend, have them come through the gates, and get back on the same train. If you don't go out through the gates and in again you won't have to pay an extra fare.

Would the bus or the Heathrow Connect be better. This is the #555 bus, right?

I'll be coming out of immigration at T1, and so the route would be either:

T1 immigration > bus stop at T1 > bus stop at T4 > T4 Underground

or

T1 immigration > T1/3 Underground station > HC to T4 Underground station

The 555 only operates every 30 minutes, and it takes it nearly 20 minutes to get between terminals.

http://www.londonbusroutes.net/times/555_557.htm

There is no bus stop at T1. The buses operate from the Central Bus Station, which is in the middle between T1, T2 (as was), and T3. You use the passages which lead to the Underground to get to it, it is physically on top of the Underground station ticket office, there are stairs leading up.

Since security paranoia set in and various airport roads were closed to public traffic, the buses have to take a very convoluted route to get around the airport. The road mileage is probably 5 or more times what the distance is by train under the airport.

There's now a dedicated "Heathrow Express" shuttle train that goes back and forth between T4 and T1&3 every 15 minutes, instead of the Heathrow Connect, so service is more frequent and reliable.

This shuttle should always be quicker (and more frequent) than the bus.

The service between T1&3 and T4 always was every 15 minutes, or at least it was supposed to be - whilst T4 was served by the half-hourly Heathrow Connect train, what happened was that it also provided a shuttle service to T123 in between departures back to Paddington - perhaps it's easiest to explain it by showing the movements of each Heathrow Connect train:

Paddington -> Ealing Broadway and other intermediate stations -> T1(2)3 -> T4 -> T1(2)3 -> T4 -> T1(2)3 -> Ealing Broadway and other intermediate stations -> Paddington

The potential problem came when the Heathrow Connect train was running late arriving from Paddington, in which case the shuttle between T4 and T1(2)3 would get cancelled to ensure that the train was on time heading back to Paddington. The new arrangement of there being a standalone, dedicated (Heathrow Express branded) shuttle train means that service disruption elsewhere no longer affects the shuttle service between T1(2)3 and T4 any more.

I reckon the OP should take the Tube and meets his friend at the T4 Tube station, as WHBM suggests above, but otherwise he should take the Heathrow Express shuttle - the bus is the long way around.

That's a plan - this is a photo of what the T4 Tube station ticket hall looks like from the ticketed/platform side of the ticket gates, and this is the same ticket hall from the other side of the gates (one can see the ticket machines and ticket windows).

^

That surely depends on whether you accept the findings of the 1967 Snaresbrook convention.

I personally fear that a reverse loop could have a Mobius effect, leaving the carriages inside-out. And where would that leave you? North Weald Basset?

It also means that more people will default to using HEx when going to/from T4, whereas previously anyone with any sense will have used HC from Paddington and avoided the extra fare and change of train. It will therefore have increased the profits at BAA.

Given the recent groupings of airline alliances at LHR, the demand for an inter-terminal shuttle is, I would think, much lower than for direct service to London.

Neil

Amazing what you can find these days!

Oh yes, I absolutely agree with that - the previous arrangement would, in BAA's eyes, have likely been seen as sullying the supposedly straightforward HEx brand by muddling things up with Heathrow Connect.

Is the man who designed the current arrangements of the Piccadilly Line at Heathrow feeling better yet ?

I really have to say the arrangements of the Piccadilly Line at Heathrow since T5 opened are one of the most bizarre of any city transport system I can think of. They are also near-impossible to describe to strangers visiting (which is surely a key aspect of an International airport).

Not generally known is the long loop from T4 going on round to T123 does swing right round westwards and underneath T5 (it passes under the taxiway between T5B and T5C). Furthermore, when built in 1984, a straight section was provided for a possible future platform, just in case a T5 was built here .....

But instead the ludicrous current arrangement was devised. It is said that when BAA first showed the design to London Underground, there was open laughter from the senior staff present. But BAA persisted, and wanted to control as much as they could (for example, the staff on the Underground station at T5, who you might think were Underground employees, are actually Heathrow Express/BAA employees, who generally show a minimal understanding of Underground questions, but can of course always recommend the Express).

Based on the map I've seen, the loop does go a fair way westwards but nowhere near the main T5 building. It passes between taxiways D and E, where T5D may be built in the future, well east of T5C.

This webpage reckons that the straight section originally provided for a prospective T5 station when the T4 loop was originally constructed is actually "over a kilometre away from the location finally decided for the terminal [i.e. T5]".

The page is somewhat inaccurate when it states that "a different part of the loop is currently being prepared to be converted into a station [for T5]", but it was obviously written some years ago when it was unclear (to the author at least) how T5 would fit in to the overall picture vis-a-vis the Piccadilly line at Heathrow. (Despite the fact it's no longer being updated these days, it remains a great website, and most of the information on it isn't going to suddenly become out of date anyway.)

P.S. Just had a look at OpenStreetMap - I don't know how accurate it is, but it shows the course of the Piccadilly line T4 loop pretty much as Reason077 states above - see here. I'd be curious to know about those early plans for T5, and when the location for the future terminal got shifted westwards.