Friday, September 02, 2005

Blockage of the Static Port

Understanding the System

To know what will happen, it is critical to understand the system, and how it is set up. The instruments involved are the airspeed indicator, altimeter and vertical speed indicator. The pitot tube feeds directly to the airspeed indicator, and the static port goes to all three.

Supposing that the static port becomes blocked, this will affect all three instruments.


We can start with the altimeter: It senses altitude based on pressure changes coming from the static port. if the static port is blocked, then the pressure in the line isn't changing. It will continue to show whatever altitude you had at the time of blockage, since that correlates to the internal pressure of the air currently trapped in the line.

Vertical Speed Indicator

The vertical speed indicator works by means of a calibrated leak. That allows it to compare the ambient pressure reading now with what it read a moment ago. Since that pressure reading from the static port is now a constant, the VSI will sense no change, and indicate a constant zero feet per minute.

Airspeed Indicator

Those two are very straight-forward. The reading on the airspeed indicator takes a little more thinking though, since both the static and pitot connect to it. The static port is reading calm-air pressure, while the pitot tube senses ram air. The air entering the pitot tube is forced in as a result of facing into the wind, so higher speed through the air translates to higher pressure in the tube.

A quick note on that: you can get a sense of the difference by sticking your hand out the window of a moving car (taking care not to hit a mailbox along the way, please). As you speed up, the air in front of your hand exerts more force. At any forward speed, the air in front of your hand exerts more force than the air inside the car.

The airspeed indicator gets its reading from a comparison of the two pressures- the pitot and the static. If those two pressures are the same, then you have zero speed indicated. In the case of a blocked static port, that pressure will remain constant, while the pitot pressure will fluctuate with true airspeed. If you remain at a constant altitude after the blockage, the airspeed indicator will read correctly. The only effect occurs after climbing or descending.

Airspeed Indicator After a Climb

Since calm-air pressure decreases as you climb, the airspeed indicator would normally recognize that, but now it doesn't. That means that the actual static pressure is higher than it should be. So the pitot and static pressures are closer together, giving an airspeed indication lower than it should. How much lower depends on how much you have climbed.

Airspeed Indicator After a Descent

The error after descending has the same root cause. Since the air trapped in the static line is at a constant pressure, that pressure will not increase as it should during the descent. So it is lower than it should be, making the comparative pitot and static readings farther apart than they ought to be. That will translate into an indication higher than normal.

So in a sense, the airspeed indicator can become an altimeter of sorts, during a static blockage.

Wednesday, August 17, 2005

Glass Cockpit

Introduction to Glass-Panel Technology in General Aviation

When referring to the term "glass cockpit" many people, including pilots, might not know what I mean. The term refers to the instrumentation in the cockpit of a plane.

The old-style, mechanical instrumentation, often referred to as "steam-gauges," is comprised of multiple different individual gauges, each with a different function. In a glass cockpit, those are largely eliminated, or relegated to a back-up/ redundancy role. Instead, the majority of the panel is computer screens, with graphical displays of the same instruments, or similar ones with more user options.

Advantages of the glass are numerous:
  • cleaner appearance
  • larger artificial horizon
  • greater redundancy in case of failure
  • more flexible and accurate navigational options
  • programmability
For students who intend to fly professionally, there is ample benefit to training in that environment. When pilots are hired to an airline position, they will be confronted with equipment that the average general aviation pilot has never seen. I'm not highly familiar with the Avidyne glass panel, but the Garmin is an excellent step toward that.

Perhaps the biggest functional advantage of newer equipment in aircraft is GPS technology. The sorry state of general aviation is that most of us fly 30 year old airplanes, with instruments that use 50 year old technology. Sometimes older. Non-directional beacons are still in use, and that technology is from the 1920's. The result is that now, most pilots who rent airplanes also have a hand-held GPS to take on flights.

The downsides to a handheld GPS are size and functionality. They can't be relied on during instrument flight, and the screens are generally very small. A large map screen on the G1000 makes for extremely easy navigation.

Many other functions are built into the system to reduce pilot workload, including flight planning help and fuel range estimates. The real difference is that for the first time, pilots of smaller planes have access to the same types of cockpit functionality that many of the large jets already use. Anyone considering flight school as a path to flying large aircraft should give serious consideration to training in the right kind of equipment. It will cost more, but the benefit is dramatic.

Biennial Flight Review

What is a Flight Review

One of the common duties of a flight instructor is conducting a BFR. A pilot license never expires. Once you get a private, commercial, or any type of license, it is yours for life, until you either do something really dumb that gets it taken away from you, or you voluntarily surrender it.

However, there are other rules that require a pilot to have some level of recent experience in order to use that license. There are two major actions a pilot must take in order to remain "current" or capable of using the license.

  • a minimum of three takeoffs and landings in that category and class of aircraft within the last 90 days, in order to fly with passengers. Landings must be done at night if you are going to be carrying passengers at night.

  • a BFR

BFR's are a requirement for currency, not simply for carrying passengers, but conducting any flight if the pilot is to have any official duties, such as pilot in command. For example, suppose a pilot earned the private license on August 10th 2005. He would then have 24 months, or until August 31st 2007 to complete the BFR requirement.

The requirement can be met in any of three different ways:

  • successful completion of a test for another pilot rating (for instance, earning a commercial or instrument rating)

  • completion of the "Wings" program

  • a flight review conducted by a qualified flight instructor

The review must be conducted in the most advanced/complex aircraft which is representative of the pilot's normal flying. If he routinely flies single-engine and multi-engine airplanes, the review would be accomplished in the multi-engine.

Contents of a Flight Review

When a pilot needs a flight review, he contacts a flight instructor. This can be any flight instructor, whether independent or working for a flight school, as long as the instructor is qualified to fly that type of aircraft. At the scheduled time, the pilot shows up with the aircraft (if he has his own), medical certificate, logbook documenting experience, and pilot certificate.

The Federal Aviation Administration gives instructors plenty of latitude regarding how a BFR is to be conducted. The requirements consist of a minimum of one hour of oral review, and one hour of flight. There are two possible outcomes to any BFR:

  • pass: when the instructor deems the pilot to be fully competent, and signs an endorsement in the pilot's logbook, allowing him to continue for another 24 months

  • more training required: when the instructor believes the pilot is lacking in some important area(s), and will require additional training

Note, that there is no "fail" option. If the pilot's performance or knowledge is not satisfactory, the time is logged only as instruction, and the pilot can either return at a later date after more study or practice, or continue the training right then, until the instructor is ready to endorse the pilot. Some BFR's are completed in the minimum time, and some require significant additional training.

The most important thing to understand is the nature of the BFR: it exists solely to help ensure that a pilot is capable before taking to the skies. Rather than being a test, it should be thought of as training for continuing proficiency.

The instructor has the latitude of determining which subject areas to test, though the pilot must be proficient to the extent of his certificate requirements (commercial-level proficiency for a commercial pilot, private-level for a private pilot). The process is remarkably similar to a checkride, except for the lack of the "fail" option. Before the beginning of the BFR, the instructor should spend a little bit of time getting to know the pilot, in order to craft his questioning in a way that is most beneficial and relevant to the pilot.

Instructor's Perspective

Often, the best way to start a review, is to ask the pilot what kind of flying he normally does, and examine his logbook. I always spend a little time getting to know the pilot first. One of my first questions is always "are there any areas of flight that you feel will need work, or knowledge that you want to specifically discuss?"

A pilot that is open, and freely expresses his confusions or areas of uncertainty, is going to spend less time and money completing the BFR. That question is not a means of tricking the pilot into giving me something to stump him on. I am there to help him succeed. I have always wanted to see the applicant pass. Sometimes it takes plenty of time to get there. Only rarely, have I ever have to tell someone to go home and study, because he would never pass it that day.

The key to remember is the endorsement. When an instructor signs his name in a pilot's logbook, that instructor is then potentially held responsible for anything the pilot does wrong later. I love aviation, and want people to succeed, and enjoy it as much as I do. But I will not sacrifice my reputation or licenses to endorse someone who shouldn't be there.

At the same time, I recognize the difference between required maneuvers and practical flying. I want the review to be reasonably passable, while still being a challenge. I want that pilot to learn something new before the end of it. So I might not specifically test turns around a point for the private pilot, or chandelles for the commercial. Some important things are not taught directly in the books. Every instructor has his own opinions on what those things are, so your choice of CFI for the review will affect how that review is conducted.