‘You’ve done it in the simulator so many times, you don’t have a real sense of being excited when the flight is going on. You’re excited before, but as soon as the liftoff occurs, you are busy doing what you have to do.’ – Alan Shepard
A running theme on this blog has been the difficulty we’ve had getting from one place to another in a timely fashion. For the western air tour, we were delayed by a day and a half getting out of Chicago. Going down to Austin we didn’t ultimately make it all the way there and had to book a Part 121 flight from Little Rock to Austin to get there for the final night of the year.
In both those cases the weather was completely flyable, but not by someone with only a private pilot license. This license gives me the ability to hurtle through the air on beautiful days, but not through clouds. With a private, we must remain 500 ft below, 1000 ft above and 2000 feet horizontally from any clouds. If those clouds are low, as they tend to be anytime you might want to fly, you have to wait for things to change.
During the western air tour we could have easily left Chicago on time, except we had no ability to get above the clouds before getting to instrument meteorological conditions (IMC). Said differently, the airport was clear enough to take off on several occasions, but we would have only gotten a short distance before running into lower clouds or rain with reduced visibility.
During the Austin trip, essentially the entire midwest was covered with a thin layer of low clouds. It would have taken a few minutes to climb through them and we would have been in cold clear air the rest of the way down.
Don’t get me wrong, we made the right decisions in flying the way we did. We changed plans and did what we could, rather than push the envelope. But it was still disappointing to not be able to fly the mission we had planned.
With that in mind, I returned to the classroom to do some work toward an instrument rating.
Instrument Flight Rules (IFR) allow a pilot to fly an airplane solely by reference to the instruments in the aircraft. In fact, one of the first things they teach is to not use your inner ear, outside visual references or, really, anything other than the instruments in the cockpit.
The primary flight instruments give only a few pieces of information, but they do so in different and redundant ways.
- Attitude Indicator – shows how the airplane is oriented in pitch and roll.
- Heading Indicator – Magnetic direction the airplane is pointed.
- Airspeed Indicator – The speed of the airplane as measured by the difference between the air entering the pitot tube and the static port.
- Altimeter – The altitude above sea level that the airplane is occupying.
- Vertical Speed Indicator – The rate at which the airplane is ascending or descending.
- Turn Coordinator – A device that displays the rate of turn, as well as whether the turn is coordinated.
- Tachometer – Engine speed.
- Compass – the magnetic direction airplane is flying.
These instruments operate on different power sources. The attitude indicator and heading indicator operate off of vacuum pressure. The vacuum pump is located in the engine compartment and is driven by the engine itself. Some aircraft have one vacuum pump, others have two and some have an electric powered backup vacuum pump.
The reason for this redundancy, is that the attitude indicator is the primary flight instrument for many phases of flight and even with all this redundancy, failures can occur. This is why we train to fly the airplane in what we call a partial panel mode. When flying partial panel, the assumption is that either the vacuum pump has failed or there is an electrical problem in your airplane. In the case of up vacuum pump failure, the heading indicator and attitude indicator would become unusable. A were some unusable, they actually present misleading information. For this reason, we generally cover them with post-its to prevent them from becoming a distraction.
In the absence of the attitude indicator, which is one of the most important instruments in the airplane, the pilot needs to learn to depend on other instruments to get the feedback he needs in order to fly safely. In the case of vacuum pump failure, this means relying on the altimeter, vertical speed indicator and tachometer to give us feedback about how the airplane is performing.
The attitude indicator gives a pilot information about the pitch and roll of the airplane. Without this we need to learn how to use other instruments to give us that feedback. In the case of pitch, we can use the altimeter to gauge pitch. In fact, while in cruise we use the altimeter to indicate whether or not we’re actually level. We can do this because pitch is an indication of whether the airplane is going up or down. If the pitch is up then the odds are that the airplane is going up. Exceptions to this are low airspeed and other unusual configurations of the airplane. But in general if the pitch is up, then the airplane is going up. If the pitch is down, the plane is going down.
The other indication we lose in the case of the failure of the attitude indicator is roll information. We can indirectly get roll information by looking at our compass. If the plane is rolling left, we’re turning left. If the plane is rolling right, then we’re turning right.
The above also hints at how we can compensate for lack of a heading indicator. Without a heading indicator, we simply rely on the compass to indicate our direction.
Compensating for vacuum failure is not all that difficult when in straight and level flight while we’re making small, corrections to capture a victor airway. However, things do get more complicated when trying to fly approach to an airport with partial panel.
The goal while flying any approach is to fly the airplane to the missed approach point, decision height or decision altitude and then go missed. If you get to those points and the airport is in sight and you can land the airplane then that’s great, that’s a bonus. But the plan should always be to fly to the mess point and then fly the missed approach.
The hard part about flying approaches partial panel is that these are fairly precise maneuvers. The stakes are also high. The pilot is taking an airplane from a safe, high, altitude with plenty of room for mistakes, to one close to the ground, ultimately touching the ground, hopefully on the runway.
The best option the pilot has is to find an area with the VFR conditions. If the pilot can find VFR the he’s back to being able to fly by looking outside the cockpit. Unfortunately, the far conditions are not always available when an instrument failure occurs.
Another of the tools the pilot can use to get to the ground safely is an ASR approach. In an ASR approach a controller tells the pilot turn left, stop turn, turn right, stop turn. The pilot just follows those directions. The controller has the airplane on a radar which allows him to see the progress of the airplane is making toward the airport. On the basis of this, he gives the instructions of the pilot needs to get to the airport in one piece.
At this point I’ve taken several lessons from a private instructor and a couple lessons from a flight school. At the flight school I also took a three-day 24-hour crash course in instrument flying and was able to pass the FAA written examination as a result.
In the last two lessons I’ve been flying a flight simulator. This is a much lower pressure and much less expensive method of gaining experience in the procedures described above. We practice in the simulator and then fly the actual maneuvers in the airplane only when the material has been learned on the ground.
During my last lesson, we worked on ASR approaches partial panel and conventional approaches. I have another lesson scheduled for later today. We’re going to go much deeper into the details of the different kinds of approaches as well as the differences between the navigation instruments that we use in order to fly the approaches.
And that seems like a reasonable place to end this entry. After we work through the navigation instruments I’ll write more about how that stuff works.