Ask Captain Lim ~ All about Aviation

Hey Capt Lim,

This is Andrew Cooper writing to you again with some more Boeing 777 questions.  I'm sure you can tell that I'm a huge fan of the Boeing 777 and an aviation enthusiast overall! 

I was talking to a corporate pilot recently and he was telling me that airliners (even 3 or 4 engines) can't fly directly over the Polar Regions on flights, say from ORD to HKG.  He told me, it is likely that all the FMS and other LCD displays would fail.  I can't understand why. At FL 350, the OAT would probably be warmer than in the mid-latitudes since you're likely above the Tropopause.  I know the airliners use True North in certain areas up North but I can't see why this would pose any problem to the aircraft.

What kind of ice protection systems are there on the Boeing 777?  I'm sure it has "hot wings" and tail area, as well as engine and windshield anti-ice system.  Anything else?  I was also wondering how far back the hot wings will protect the wings?  It seems like hot wings actually could make icing worse when the super cooled droplets first hit the leading edges. They will remain liquid but when they slide back beyond the leading edges, the moisture will freeze very far back. It would then be impossible to remove them since the heat doesn't transfer that far back unless the whole chord is heated. 

Also, as I'm sure you know that freezing rain and drizzle are the worst.  Pilots of light singles and twins are told to avoid them like the plague!  If these conditions were at your departure or arrival airport, would you still fly?  If you would, would you fly the approach with less or no flaps and several knots faster than usual?  You might remember about 10 years ago, the ATR 72 had crashed in Indiana, USA, because the auto pilot was engaged and in severe icing, it got behind the boot. It caused an aileron reversal and all the sudden, the autopilot disengaged violently. It then caused the plane to spin out of control.

Thank you very much again for all your time and this wonderful site!  Hope you had a nice holiday too.

Andrew Cooper.

Hi Andrew,

Although airliners could not fly from Orlando to Hong Kong (probably due to the distance) it is not true to say they cannot fly the polar routes to save flying time.  In fact, the cross-polar routes are already used by United and Northwest Airlines for scheduled nonstop services between Chicago and Hong Kong (7,786 nm) and Detroit and Beijing, using Boeing 747-400's. Continental Airlines recently added the Newark to Hong Kong polar route (7,337 nm) using a Boeing 777-200.

According to a polar route study, the traditional route from Detroit to Beijing involves a flight of some 6,600 nm. Now, by flying the polar route, the distance is reduced to 5,700 nm, saving about 900 nautical miles off the trip. The only problem is, in-flight emergencies may require a diversion to remote airfields in Siberia where, in the winter, temperatures can plummet to -70 degrees F.

Again, it is not true that the FMS (Flight Management System) or LCD (Liquid Crystal Display) would fail.  Yes, above about 78 degrees north, pilots would use True North to navigate for this is also the limitation of the FMS.  At FL 350, the airplane would be flying above the Tropopause (as you rightly said), and the outside air temperature would be in the region of a constant minus 56 degrees Celsius. This temperature is quite normal and the LCD would continue to display.

On the Boeing 777, the ice protection system is automatic and caters for polar route operation.  Your description and fears of what might happen to the wings, engines, windshield as a result of icings, is unlikely when compared to the light and twin engine airplanes.  On the ground at the departure or arrival airports, the normal winter operating procedures would apply.  The airplanes would be deiced prior to take off. Freezing rain or drizzle are flying hazards and pilots would delay or avoid them altogether during the take offs.

The choice of flaps and speeds would be determined by the airplane take off weight.  The only difference to the normal procedure in icing conditions would be to delay selection of the take-off flaps.  This is to prevent the flaps from getting iced up at the hinges or gaps if there were water moisture and were selected too soon.