A reader asks, “I heard Chinese and Russian air space uses the metric system while most other countries use the imperial system of measurement. Is it alot of trouble converting the different system of measurement? I remember a Air Canada 767 having to make an emergency landing due to running out of fuel from wrong metric conversion. That won’t happen with Cathay?” — Tomcat1

Two great questions that I wanted to answer in my blog, one at a time. The first issue deals with metric flight levels and the second issue deals with metric fuel volume. I’ll answer the flight level question below, and the fuel question in the next blog entry here.

Most of the time, you and I hear the captain come over the P.A. and say that we will be cruising along at 37,000 feet. Because he told us a value in feet, it makes sense. This is because ICAO, or International Civil Aviation Organization, the world standard on aviation issues, has deemed that altitudes and flight levels will be measured in feet. There are some nations though, that use metric altitudes and flight levels and don’t follow ICAO rules and suggestions. CIS countries (former Soviet countries dissolved in 1991 that have names that end in “stan”, like Uzbekistan) and Russia and China assign altitudes in meters instead of feet. The captain on a flight traveling from Moscow to Beijing might say we that we will be traveling at 10,600 meters. Huh? How high is that?

As a side note, there are altitudes and there are flight levels. In North America, below 18,000 feet is called an altitude, and 18,000 feet and above is called a flight level.**

The issue then becomes, when transiting the airspace of a country that uses meters, there has to be a transition from feet to meters for our assigned altitude. This occurs all the time and happened on my last flight from Anchorage to Hong Kong, as we passed through Russian airspace. Before we crossed into Russian airspace, we were flying at 38,000 feet, or flight level 380 (three eight zero). The American controller asked us what our requested flight level was in meters and we told him 11,600 meters. He then passed that on to his Russian counterpart, and when we crossed into Russian airspace, the Russian controller told us to climb and maintain 11,600 meters. This metric altitude is equivalent to 38,100 feet, so we climbed 100 feet.

Often times, this transition is done outside of radar contact, meaning we are not on anyone’s radar scope. The onus is on us to make the proper correction so we don’t hit an oncoming aircraft going the other direction. To make sure this is done properly, we have a small chart that we always pull out, even though we know what it says, and it tells us the metric values and their equivalents in feet. Another nice little handy dandy thing in the 747 is a meters button on the instrument panel. When it is pressed, our digital altimeters show both feet and meters together, making this procedure a no brainer. However, we use the chart, even though we have a meters button, because we always set our altitude in feet, even in a metric environment. Why? Easy: The autopilot only takes inputs as feet, in 100 foot increments. In some situations, the metric equivalent could be right in between these 100 foot increments, at say 39,450 feet. If that is the case, do you set 39,400 or 39,500? So that every Cathay pilot is on the same page, we set the altitudes given us by the conversion chart, and keep meters selected on our altimeter to double check our altitude in meters. That way, the chart does the rounding for us and it’s even less of a no brainer.

The great thing about no brainers? They are hard to mess up, so the procedure is safe and effective. Now, has the other pilot, in his 747, screaming along at 600 knots, coming right toward us in the opposite direction, has he set his altimeter correctly? Ha ha! To protect for that, there’s TCAS.

TobyLaura.com

** A flight level is an altitude where altimeters are set to a standard barometric setting, 29.92 inches. In the U.S. and Canada, this is done at 18,000 feet and higher, so that below 18,000 is called an altitude and 18,000 feet and above is called a flight level. Other countries have different transition levels, where the pilots adjust to the standard setting (in Hong Kong, it’s 9,000 feet) but the principle is the same. Closer to the ground, we want our altimeters adjusted for local barometric pressure, as this can affect what the altimeter reads. With the local pressure put into the altimeter, the more accurate it is at telling us our height above the ground. Air traffic control lets us know what this baro pressure is. Up away from the ground, to help everyone to be separated by perfectly equal amounts of accurate airspace, we set a standard of 29.92, keeping everyone’s altimeter reading the same value, no matter what the local pressure is. Ground contact isn’t a factor, and altimeters give us an accurate reading, not above the ground, but a standard plane, at 29.92 inches of mercury. This allows tight vertical spacing of aircraft, because with everyone’s altimeter reading the same altitude above the same level plane, aircraft can safely fly more closely together.

Have you ever wondered what would happen if you were a passenger on a long flight over the Pacific and something terrible happened? I know I have, and like most of us, we probably envision treading water for a long time, or sitting in a life raft because the water is too cold for survival. (In the North Pacific in the winter, the water is survivable for about four minutes without protection or a lifeboat.) Fortunately for today’s passengers and crew, this possibility is quite remote, thanks to many modern conveniences like excellent communication equipment, well designed and highly reliable aircraft engines, and safety procedures that are well thought out.

I can think of three major emergencies that we as pilots can plan and prepare for, that if the safety procedures are followed, are completely survivable, even when there are thousands of miles of ocean below the airplane.

These are: Fire, Engine Failure, and Cabin Depressurization.

There are many other things that could go wrong, but they are not as severe as these three biggies. Bigger than these, like the wings falling off, either usually don’t happen or aren’t survivable anyway, so why plan for or worry about them?

An onboard fire is probably the worst of the big three because it can quickly escalate from harmless to deadly in just a few minutes. Recall all those warnings about tampering with the smoke detectors that you hear prior to departure? Yeah, those are deadly serious — no pun intended. The cargo compartments will seal themselves shut in the event of a cargo compartment fire to starve it of oxygen and fire suppression systems like Halon extinguishers take care of the rest of the fire. The cabin is a bigger problem because unless the fire is in a galley or lavatory trash can, it requires people like flight attendants to fight it. There have been several major fire disasters because the cabin caught on fire, like this Air Canada DC-9 and this South African 747 Combi (A combi 747 is one where the back half of the plane is cargo, and the front half is set up to carry passengers.) I’m sure that the lack of passenger smoking on planes has saved many lives.

But what about the cargo planes, like the one I fly? The cargo section of the main deck of the 747 is cavernous and there is no way to have enough Halon to put out a fire on that type of scale. But surely we have a way to fight it while it’s three a.m. over the Pacific or Himalayas, right? The answer is yes, and it’s actually a better system than in the passenger versions of the 747. Because we don’t have to worry about keeping 400 people alive down below us, we depressurize the entire airplane while wearing oxygen masks, to starve the fire of oxygen. When we get a fire warning, we put on our oxygen masks and raise the cabin altitude to 25,000 feet, where there isn’t enough air to burn an open flame. Once the fire is out, we lower the cabin back down to five or six thousand feet and take off our masks. It’s a simple system that should prove to be very effective, however, I hope I never need to test it.

Along those same lines, another major problem that we can deal with effectively is cabin depressurization. If our plane can’t maintain pressurization, then we can’t maintain consciousness and everyone goes to their final sleep. Contrary to what some believe, aircraft don’t carry large tanks of oxygen to allow people to breathe, they simply pack air into the cabin to provide pressure similar to sea-level pressure. See, the ratio of oxygen in the air, 21% is the same at sea-level as it is at 40,000 feet, there just isn’t enough pressure in the atmosphere to breathe it in at high altitudes. Aircraft don’t have to constantly supply oxygen, it is already there at 21%, they just have to make the pressure available for us to be able to breathe. They do that by taking high pressure air off the engines and sending it into the cabin. The cabin’s “altitude” is controlled by how much of that pressurized air we let out, with a special valve called an outflow valve. As the valve opens, the pressure in the cabin lowers, and as the valve closes, the pressure gets greater inside the cabin. At high altitudes, we need lots of pressure to maintain breathable air, so at cruise, the valve is mostly closed.

When that system fails, or a hole gets blown into the side of the cabin, we lose all our pressure. The masks drop and provide air for a little while, but only for a few minutes at high altitude. We have to descend down to more breathable air, but doing that increases our fuel burn dramatically. On our Cathay 747’s, we first descend to 14,000 feet, until all the oxygen in the masks are depleted, and then we descend to 10,000 feet, where everyone can breath normally. Our fuel burn will be around 50% more down at 10,000 feet, so if we are out over the Pacific, our destination is off the table. We will have to go to an en-route alternate, decided upon by using our point of no return, or PNR, described in the last blog here. Again, we always have to have enough fuel when we depart, to have a depressurization at any point along our route, and still be able to reach a suitable alternate.

And finally, there is the little matter of engine failure. Do any nervous flyers ever worry about that? I didn’t think so :o) No, it seems everyone’s fear is engine failure, especially when traveling over such huge expanses of water. The good thing about the 747 is that it comes with four engines, so there is little chance of major trouble. But even superb aircraft like the 777 that only has two engines doesn’t cause much concern for alarm as engine failure is so remote. These engines are not like a car’s engine. They are millions of dollars worth of precision, and because they rotate, there are very few parts that wear like engine parts wear, and their maintenance is much improved over the maintenance you and I give our cars, for sure!

However, with that said, failures do occur, and when they do, pilots need to be ready for them. Much like the last blog entry described about PNR’s here, we have a three engine PNR, where if one fails prior to a certain point, we know we’ll need to return to a certain airfield, and if it fails beyond that point of no return, we will be able to continue to another airfield. This is because we now may not have the fuel to continue to our destination.

Why? Because we actually burn more fuel with three engines than with four. It sounds counter intuitive, but think of it like this: When we go from four to three engines operating, we now have less thrust. Less thrust means we can’t maintain the same altitude, and have to descend a few thousand feet. This is because the higher we fly, the more thrust it takes to keep all that weight up in the sky and when we lose some of that thrust, we start to slow down. If we lost an engine and didn’t descend, we would slow down beyond the speed at which our wing would be able to maintain lift, and we would stall — where the wing can’t produce enough lift for the weight it is having to carry. The trouble is, when we do descend, we burn more fuel and that is why losing an engine will actually cause fuel troubles. Also, I believe the synergy affect applies here, too. The thrust from four engines is better and more efficient than the increased thrust of three, making up for the lost engine, if the aircraft maintains the same weight and altitude.

So, I write this to give you a little bit of insight into what we plan for in the 747 as we get ready to cross large expanses of inhospitable terrain, either mountains or oceans. When crossing the United States, there are so many airports to duck into if trouble pops up that there isn’t much planning to do. But when there are vast distances between places of refuge, proper planning is essential. Never fear, as even with the three biggest troubles that can occur, there is always enough fuel to get to a suitable landing field, because if there wasn’t, we wouldn’t be taking off in the first place. Cathay doesn’t pay me enough to take that type of risk!

TobyLaura.com

Now this blog entry could be about the interest rate on your bank account, buying things at Cord Camera, or even a scary movie. The point of no return conjures up thoughts of entering an old, spooky house, with cob webs, knight’s armor, and paintings on the walls where the eyes follow you as you slink down the long hallway, and pipe organ music playing demonic chords. That could all be true, but I want to talk about what the point of no return has to do with crossing large bodies of water, like the Pacific, while flying (enter more creepy pipe organ music).

Even though the term point of no return sounds ominous, and nervous flyers might think it would be one more reason not to fly, it really has everything to do with safety. On a typical flight from Hong Kong to L.A. as we fly across the Pacific, we depart the Japanese coast and head out for the West coast of the U.S. Because there is only water beneath us, or because there are limited airports available to us along the Alaskan Aleutian Islands, we come to a place in the sky where we no longer can return to the airports in Japan based on the amount of fuel we have remaining.

On our flight plan, we have lat/long coordinates that tell us when we’ve passed the point of no return, based on two airports, say Narita in Tokyo, and Vancouver. This point is often not equidistant between the two cities because of how the winds will affect a turn-around. However, we have this point of no return, or PNR, calculated for us so that in an emergency, we don’t turn back toward an airport we can’t get to based on fuel remaining. Prior to reaching the PNR, we tell ourselves that if we lose an engine, we will return to Tokyo, and once we’ve passed the PNR, we will continue to Vancouver. We always have enough fuel to get to one of these en-route alternate airports, or ERA’s. We can’t depart on our trip unless we have the fuel at any point along our route to get to a safe landing airport, and the PNR helps us to make a better decision on where to divert in an emergency.

The PNR is also helpful because the two airport choices may not be as friendly as Tokyo and Vancouver. They may be Cold Bay (shown on the left) and Shemya, both in the Aleutian Islands. Neither are wonderful places to visit, especially in the winter time, but I’d rather divert to Cold Bay because Shemya is a postage stamp in the middle of the North Pacific. The PNR is important because even though we may want to go to Cold Bay, if we’ve passed the PNR, it’s hello balmy Shemya for us.

TobyLaura.com