How safe is glide landing?

[Spectator]

How is this going to affect landing safety? Is this introducing more holes in the cheese? I'm not against savings, indeed the industry needs them, but how long before we see the effects...

Using less fuel by idling the engines, the landing approach is less expensive, less noisy and emits less carbon dioxide than the conventional way of bringing planes to the runway.

The longer duration is an issue tackled with the innovation used by Novair that shortens landing time with a satellite-guided approach in a downward curve.

It's the beginning of an evolution from a system based on rules to a system based on efficiency," says Lars Lindberg, head of Swedish aerospace company Avtech that developed the technique.


Although impossible in poor visibility, it also fixes an accurate touchdown time and passengers offer good reports.

http://travel.iafrica.com/flights/2099100.htm

[Peter Kesternich]

Well - I would say this is another classic example of a misleading article because the journalist is not an aviation expert. The way I read the quotes and the article, we are not talking about landings or even approaches but DESCENTS. What is described here is an extended, computer- and GPS-supported version of the low-drag low-power approach already practiced in many countries.
Rest assured, as soon as the aircraft crosses the final approach fix, it will all be back to normal and safety will be unaffected.

[Spectator]

Thanks

Thanks Peter for your comment. I am not aware of the extent of this practice (i.e. how many airlines do it) or to what extent they practice it (i.e. how drastic their fuel saving initiatives are).

What I was thinking of was what happens when a plane encounters an emergency and requires full power suddenly near the end of its decent when the engines have been on idle for a relatively long period? What are the possibilities of previously unseen issues cropping up, such as frozen fuel lines, etc?

Obviously if this practice is widespread already, and only being reported now as a "press release" for the GPS guidance system, then I would assume that issues would have been seen already.

[Peter Kesternich]

Well - engines have been reduced to idle for a long time in the descent, so technically and safety-wise there is no problem. Even at idle thrust, the engine will consume a minimum amount of fuel just like an idling car engine, so there's always movement in the fuel lines and after all fuel is heated using various methods to prevent freezing.

[Evan]

Peter, I believe Spectator is referring to BA38, which begat a provisional procedure on Trent powered 777's to avoid extended idle thrust on decent. The current theory is that ice had formed on the fuel/oil heat exchangers due to extended flight in very cold temperatures combined with low fuel flow for extended periods during idle descent. Other theories have suggested that the ice formed upstream of the high-pressure fuel pumps. In any case it seems to have only affected Trent equipped 777's, so it's not a universal issue.

But still, considering the mysterious nature of the incident and the difficulty in positively identifying the fault, I think he has a valid root of concern. Apparently, under certain rare circumstances, jet fuel at extended low flow rates can ice up in tight places.

The other point, about spool-up time in an emergency, was aptly demonstrated by Turkish Airlines 1951, but, of course, that was during approach, not descent. Still, I would like enough standby thrust to be available for things like collision-avoidance during descent (or terrain-avoidance for the alpine impaired).