Ask Captain Lim

Hello Captain Lim,

Could you please clarify the following...

1. Suppose there is a major breakdown in the on-board computers and your entire PFD/ND/FMS/EICAS have gone blank how would you navigate the plane and land?
What happens if you were over the mid-Atlantic?

2. With the same situation as above, if you had very poor visibility and you cannot see the ILS information in the PFD/ND, how do you land the airplane? Do you practice this scenario?

3. If in the same situation, you cannot see any system malfunctions in the EICAS, how do you detect any failures and deal with them? Do you practice multiple system failures?

Thanks and warmest regards,

Srihari J

Hi Srihari,

Here are the answers to your queries. I know you have a lot of technical questions on the Boeing 777 for me. To be beneficial to the other readers, I will answer them from the point of view of someone of lesser technical background than you have.

1. Let me explain what is PFD/ND/FMS/EICAS first before I delve into the answers. PFD (Primary Flight Display) is the most important flight instrument display in the Boeing 777, without which it would make flying the airplane more difficult. The ND (Navigation Display) is equally important because it displays many important information necessary for the pilot to navigate from A to B. The FMS is the Flight Management System which consists of the two FMC's (Flight Management Computers) and can be described as the 'brain' of the airplane. EICAS is the Engine Indication and Crew Alerting System which alerts the pilot of any malfunctions in the Boeing 777.

What happens when all these important indications went blank from the LCD (Liquid Crystal Display)? Good question! In my Website topic on the safety of the Boeing 777, I mentioned that this airplane has many built-in redundancies and backups. So when one system fails, another one will take over automatically or by pilot's action because many of these major instrument failures are foreseen by the airplane designers. There are 6 flat panels - LCD Units consisting of 2 PFD's, 2 ND's and 2 Center Display Units. When one PFD fails or goes blank, it will automatically switch over to the one beside it. Now what happens when the Captain's PFD and the ND, which are side by side, goes blank? No big deal! The Copilot's PFD and ND would still be available. The Captain merely hand over the flying to the Copilot! Now you know why the Copilot's role is so important in an emergency!

What happens when the FMS fails? There are 2 computers providing many flight
performance information to the airplane. When one computer fails, the next one will take over automatically. When both computers fail, there is still the alternate degraded system when the pilots have to use their brains to supplement this crippled system. This is not a big deal too because pilots have been trained to cope with dual computer failures as well!

When EICAS, which are displayed in the upper center LCD fails, it would switch over to the bottom center LCD either automatically or manually by the pilot. So when all these systems fail in mid-Atlantic, it is still possible for the pilots to navigate and land the airplane safely at the destination!

2. I believe you have read my previous topic and answers on the Auto Landing System where pilots are trained to recognize emergencies at the critical moment prior to landing in poor visibility. Anyway, the odd of failure in this critical phase of the flight is very remote. Remember that, when the airplane is locked onto the Instrument Landing System in an autoland approach, the logic of the system automatically goes further into a mode that would take care of failures of the critical components. What happens is, the electrical power automatically isolate into three independent sources to power the 3 auto pilots. This means that failure of the Captain's flight instruments would not affect the Copilot's side whatsoever!

Nevertheless, and in the worst case scenario, a pilot would still abort a landing using the standby flight instruments if he notices any instrument failures that would affect the ability of the airplane to safely complete the landing. He would not land but divert to an airfield with better visibility.

3. The EICAS is normally displayed on the upper center display unit. If the unit fails to display the EICAS, it automatically moves to the lower center display unit. So any malfunctions would still be displayed and dealt with accordingly.

Multiple system failures are being regularly practiced in the simulators to ensure pilots are familiarized with the various emergency procedures and drills.

Now you know why this US$170 million Boeing 777, with so many safety features, is one of the safest airplane in operation today!

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