Big, Bigger, Biggest (Five, 8pm); Hotel Babylon (BBC1, 9pm); Horizon (BBC2, 9pm)

WHEN Croydon Airport, near London, was the country's main airport in 1920, pilots were flying by the seat of their pants as they found their way home using landmarks.

"Oh, there's the Tower of London, left hand down a bit. And isn't that Buckingham Palace? Turn a bit to the right". That sort of thing.

A collision on April 7, 1922, made them think again. New technology, using radio bursts from the aircraft, enabled people at the airport to establish the flight path.

That was the birth of air traffic control.

Then, Croydon had about 60 flights a week. Today, Heathrow handles up to 100 flights an hour.

Big, Bigger, Biggest won't do anything to appease those opposing airport expansion, but will send aviation enthusiasts into orgasms of delight with its endless list of facts and figures about Heathrow's Terminal Five.

The new terminal cost billions to build, but the construction was far from plane sailing, with 19 years of work going into the three huge terminal buildings.

The programme uses the terminal to trace the history of airports, explaning why and how such aspects as runways, baggagehandling, terminals, moving sidewalks and control towers have developed to keep pace with developments in flying.

As aircraft have grown bigger and passengers increased, so airports have had to change.

That includes using a new kind of concrete underfoot to support the new seven-storey tall Airbus A380, and developing personal rapid transport, which means driverless pods - that's robot taxis to you and me, ferrying people around airports quickly and efficiently.

The terminal also has an amazing automatic baggage-handling system. Run by robots, it has the advantage of not taking a tea break and can move your bag from check-in to plane in less than 15 minutes.

In the tradition of Five's programmes on moving big buildings, we see the control tower being built on the edge of the airport and then moved into position in one piece on three transporters designed to carry a space shuttle.

Passengers on the aircraft taxiing to the terminal must have thought they were seeing things as the tower moved across the tarmac in front of them at 2mph.

LET'S hope none of the passengers is booked into Hotel Babylon, the BBC's glossy and glamorous, but ultimately tedious and unbelievable, drama series.

New manager Jack (Lee Williams) is told he needs to be part conman, part showman.

At present, he's total drip. Faced with John Barrowman at full throttle as a director filming at the hotel, he'd do best to run and hide in the nearest cupboard.

His staff are uncontrollable. The barman goes around doing De Niro impersonations, although I agreed with the verdict that "You sound like a Spanish Mr Bean".

Amid all the corny chaos, the storyline about the dying girl unable to tell her nearest and dearest seems woefully out of place.

HOTEL Babylon is a show you watch and instantly forget. Horizon's documentary How Does Your Memory Work? offers a more serious examination of memory loss.

John, born prematurely and whose memory circuit never fully developed, cannot bring his past to mind. He relies on his mother and photographs to remind him of his past.

His condition means he is trapped in the present. Unable to draw on the past, he can't look to the future. Think how inhibiting that is.

Genevieve's memory was affected by an assault. She is given drugs, not to erase the trauma, but to tone it down and let her to get on with her life.

Sixty-year-old John is shown on his daily run. He looks normal enough, but seven years ago he was diagnosed with Alzheimer's. "The future - forget it," is his advice.

Outwardly, he is fine but his wife tells how it affects every single thing in his life.

He can't even get a glass of water. If he remembered where the tap was, he wouldn't remember how to turn it on.

His wife brings home the situation as she likens him to a tree with Dutch elm disease - dying from the inside out.