Ask Captain Lim - Questions on vision problems, ADIRU and long haul flights.

My name is Ruslan. I am 18 years old. I want to start my flying career from Private Pilots' License (PPL) to my favorite aircraft, which is Boeing 777. My hobby is aviation and I fly Boeing 777 in the flight simulator 2002/2004.

Your site is great and informative. I read most of your FAQs and I think I know the airline you are working for.

I have many questions but now I want to ask only three. First, medical, second, technical and third, on the pilot.

1. I have normal vision but after a medical check the doctor told me that one of my eyes can see better that other and later on when I decide to take up flying, I may have problems with it. In your FAQs on "How stringent are pilots' medical" I do not understand what these requirements means :-

- "Distant visual acuity of 20/20 or better separately with or without glasses"
- "Near vision of 20/40 or better with or without glasses"
Can you explain these numbers? Can airline pilot like you wear glasses and can you explain my case? (it's very important for me!)

2. Can you briefly explain what is the ADIRU system on the Boeing 777?

3. When you fly long haul routes, especially when the plane is cruising on autopilot, is it difficult for you and your first officer to concentrate on instruments for long time, for example, 5,6 or 7 hours? What are you allowed to do beside flying the plane in cruise?
Please e-mail me. Take your time and thank you very much.

Best wishes and safe flights always.

Ruslan

Hi Ruslan,

1. The medical standards may vary in your country but generally, the rules are more relaxed today. What it means is that, as long as your eyes can be corrected by glasses to a normal vision of 20/20 (or 6/6), it is acceptable for commercial pilot training. In fact, I do wear glasses for reading as well as for distant vision. A near vision of 20/40 or better with or without glasses is a lower standard than 20/20. As I am not an eye specialist, I cannot explain further on the exact requirements. Check it out with a specialist if you are still uncertain.

2. ADIRU stands for Air Data Inertial Reference Unit. Briefly, this unit makes use of laser gyros and accelerometers to sense angular rates and linear acceleration in the air. The computers would make use of these information to give the pilots many data to enable him to operate and fly the airplane safely. Some of the information include the airplane's attitude, such as whether it is turning or climbing, its speeds, position, heading, wind velocity and rate of climb or descent. So it is a very important unit, without which the airplane would be rendered useless to go anywhere. Of course, there is a backup known as the SAARU which would come in automatically when an ADIRU fails in the air.

3. On a long haul flight, there are two sets of crew, meaning 2 Captains and 2 First Officers. The flying duration is divided equally. When the airplane is cruising, it is on auto pilot. Flying is alternated between the Captain and the co-pilot. So when a co-pilot is flying a particular sector or route, he is known as the PF (pilot flying) and the Captain is the PNF (pilot non-flying). Whoever is the PF is responsible for managing and flying the airplane safely whereas the PNF's duties is merely supportive and does all the position reporting. Both would continue to monitor all the systems to ensure that they are functioning normally. Even though the co-pilot may be the PF, the Captain has the overall responsibility of the flight. It is not true that the PF must continually focus on the instruments at all times, just like you see one flying a basic airplane. He scans all the instruments intermittently because the auto-pilot is controlling the airplane and he is allowed to do some light reading during the cruise. You can read more of this under my topic on 'a day in the life of a pilot' in this site.