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Delhi’s fog disrupts flights across India every winter. With ILS and autoland, it doesn’t have to. The tech to land aircraft in zero visibility is mature and safe. But certification and pilot training are taking time.

| Updated on: Mar 11 2010, 12:13 IST

Delhi's fog disrupts flights across India every winter. With ILS and autoland, it doesn't have to.

Seated next to me in GoAir's so-called 'business class', a businessman described his switch to low cost carriers. He used to fly Jet Première, till he sat through three fog-grounded flights. "Once I sat in the plane - in business class! - and watched low-cost carriers taking off!"

We swapped notes on IndiGo's 100 exit row upgrade and Go's 1,000 biz-class upgrade... and how I went from platinum on Jet's frequent-flyer programme down to 'blue plus'. That's after moving to Indigo... thanks to their on-time record, prices, and sandwiches.

Keeping passengers warm in Delhi's biting winters is the hot topic of the fog. And why it affects some flights. And why we go though this horror every year, while the world's airports thrive. And why the low-cost carriers are doing so much better...

Delhi airport had the right equipment this year, and the worst results. During 20 days in January, when the fog peaked, 200 flights were diverted, 350 rescheduled and 339 were cancelled. Jet managed just 20 takeoff/landings from Delhi in those 20 days, while Indigo did 80 - with far fewer scheduled flights. Kingfisher and Air India did much better. So why the differences, when they all claim to be Cat-III ready?

A friend and aviation columnist asked around, and found out that most of Jet's fleet and pilots are merely CAT IIIA-ready, while all of GoAir's and IndiGo's planes and most of their pilots are CAT IIIB-ready (see So are most of Air India's planes and pilots.

So what is all this Cat III stuff anyway?
That's the category of instrument landing system. ILS gives precision guidance to aircraft, using radio signals and lighting arrays. Useful in fog. A pilot will follow the ILS 'glideslope', a path outlined by the radio beacon, until he reaches the decision height and RVR (runway visual range) at which he must either clearly see the runway or its lights - or abort the approach.

The categories of ILS describe the tolerance and precision. Category I allows a minimum height of 60 metres and RVR of 550 metres. Not much use in dense fog. CAT II needs just 30 metres height and 350 metres RVR. Better, but still no go in Delhi winters.

Then there's Category III. CAT IIIA takes us down to 200 metres RVR. Good for most conditions, but not Delhi's peak fog. CAT IIIB drops the minimum height to 15 metres, and the RVR to 75 metres. Good enough, except in zero visibility. Delhi has a CAT IIIB ready runway. But the plane and pilots also need to be certified, to land or take off in those conditions.

And then there's CAT IIIC. That lets you land in zero visibility with zero decision height and RVR. You can land blind, even cover up the cockpit windows with black paper, sit back, and land. In practice, no airport allows CAT IIIC landings yet, because of practical issues - like how do you taxi off the runway if you can't see a thing?

Pilots can't do much manually in dense fog. I can't even take a brisk morning walk without bumping into people and trees, let alone drive. So aircraft use automatic landing, or Autoland. Even after touchdown, the system runs the aircraft: spoilers, autobrakes with ABS, and thrust reversers kick in... When it slows down, control is handed over to the pilot, who then has to taxi the aircraft very carefully, and avoid bumping into other aircraft...

With Autoland, "we usually sit back and watch the plane land," says my pilot friend. So today, in those Hollywood scenarios - oops, both pilots died! - a passenger could actually be instructed to land a modern passenger aircraft.

How safe is all this?
In Die Hard 2, terrorists took over the airport... a la Hollywood, they entered commands into an ATC computer to lower the ILS beacon by 200 feet... and a passenger jet crashed. Stuff and nonsense. The glideslope has to terminate on the runway touchdown zone. Even if someone changed its slope, pilots have GPS, radar altimeters, ground proximity warning systems, and brains.

Both ILS and autoland systems are designed so that if the rare failure occurs, it is detected, and acted upon. The technology to land aircraft in zero visibility is mature, and safe. Yes, installation, maintenance, certification and pilot training take time. But it's possible to avoid the kind of flight disruptions that Delhi, and thus India, sees every winter.

I'm hoping this winter will have been the worst of them: that the benchmarks set by a few airlines will force the others to follow, and to use the technology sitting with them.

The author is chief editor at CyberMedia, publisher of 15 specialty titles including the gadget site . ,

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First Published Date: 06 Mar, 15:39 IST