Sunset to Sunrise: Night Flight Techniques

Moorabbin.

Introduction

Night flight is magnificent. It is smooth, uncluttered, and easy, provided you learn the correct technique and you fly regularly. Night flying technique is the same as day flight, except you probably will not have a visual horizon. There is, therefore, only one way to fly at night: by the instruments. However, there are two ways of navigating (visually and by NAVAIDs) and two sets of rules and procedures (IFR and VFR). Each has its own pros and cons.

Why Fly at Night, Especially in a Single-Engine Airplane?

Some of the aspects that can make night flight such a pleasant experience include smooth conditions, good visibility, reduced wind, traffic, talking, and thermal activity, wonderful sunsets (and sunrises if you are an early riser), and beautiful patterns of stars and lights. Moreover, there are the added advantages of increased aircraft utilization, better takeoff and climb performance, better visibility (greater distances), fewer birds (although you may encounter bats and other animal activity), easier and faster service at FBOs, and more readily available aircraft rentals. But night flight has its potential hazards—you may not see an embedded thunderstorm inside a stratus cloud, the ADF needle can give false indications at night, and there are few lights and many illusions over sea, desert, and mountains. Like all forms of flight, night flight should be approached with due respect, but more so because there is less room for error or inaccuracy and fewer escape options.

Single-engine flight at night can be quite safe. Some pilots tell tales of engine noises, fluctuating oil pressure, and rough running at night or over the sea, but the engine does not know that it is night, or that it is over mountains or water. So why does it seem to make strange noises? I don’t know—perhaps we hear what isn’t there because of heightened sensitivity. If you know the engine’s maintenance history and have personally checked the fuel and oil, the engine should be very reliable. However, realize that a forced landing may not be an option in some areas. Choose your route with this in mind. A track with rivers, beaches, lakes, or straight, lit highways gives some chance of survival. Your autopilot, attitude indicator, and turn coordinator become as important as the engine. A powerful and reliable engine is useless if you have no attitude reference.

Night flight in a multi-engine airplane is potentially safer than in a single-engine one. However, engine failure and asymmetric control at night are demanding exercises in themselves, especially immediately after takeoff. Do not forget your emergency self-brief for these possibilities.

Equally important is the built-in redundancy in the lighting, electrical, and instrument systems. Unless you are current, confident, and competent at partial panel instrument flight, choose an airplane with a standby attitude indicator, if available.

Night Visual Flight

Night flight is not visual flight despite being called night VFR and the weather conditions being called night VMC. The official definition of night flight relates to weather conditions or to regulations and rules that apply, but not to the techniques of controlling the airplane.

This book highlights the hows and the how nots for safe night flight. Use the autopilot—it can be a good friend, but unlike your best friend, do not trust it absolutely. Keep a weather eye. The same advice applies to the GPS.

If you fly smoothly, confidently, and regularly, you will enjoy night flying.

Part 1

Refresher

Chapter 1

Instruments and Systems

The definitions and regulations regarding day visual meteorological conditions (VMC) and night VMC do not specify a clearly defined horizon. Night flight is instrument flight—make no mistake. If there is no visual horizon, you are flying on the clocks. During the day in reduced visibility and over level terrain, you may get away with a vertical reference below the airplane as a guide to airplane attitude and flight path. At night, it is too risky. Uneven distribution of lights and stars gives subtle but misleading cues as to which way is up, which way is down, and whether or not the airplane is level. You must fly attitude on instruments and be able to do so competently when talking on the radio, reading charts, writing down instructions, and looking for ground features and other traffic.

Flight instruments fall functionally into three categories: pressure instruments, gyroscopic instruments, and compass instruments. Pressure instruments include the airspeed indicator (ASI), the altimeter, and the vertical speed indicator (VSI). Gyroscopic instruments include the attitude indicator (AI), the heading indicator (HI), and the turn indicator or turn coordinator. Compass instruments use a magnetic reference. In support of the flight instruments are the pitot-static system, the vacuum system, and the electrical system. All of these are brought together by the greatest aid to the pilot—the autopilot.

Pressure Instruments

Airspeed Indicator

The airspeed indicator displays indicated airspeed (IAS). Indicated airspeed is a measure of dynamic pressure, which is the difference between the total pressure of the pitot head and the ambient static pressure. The airspeed indicator will have the following specific speeds marked on it:

VS0—stall speed at maximum weight, landing gear down, flaps down, power off;

VS1—stall speed at maximum weight, landing gear up, flaps up, power off;

VFE—maximum speed, flaps extended;

VNO—maximum structural cruise speed (for normal operations); and

VNE—never-exceed speed (maximum speed, all operations).

Figure 1-1 ASI.

In addition to showing indicated airspeed, some airspeed indicators are able to show true airspeed (TAS). These ASIs have a manually rotatable scale to set outside air temperature (OAT) against altitude, allowing the pilot to read TAS as well as IAS.

Figure 1-2 IAS/TAS indicator.

Airspeed Indicator Errors

Density Error

Density error occurs any time an airplane is flying in conditions that are other than standard atmospheric conditions (ISA) at sea level. This is why the airspeed indicator does not indicate TAS.

Compressibility Error

Compressibility error increases with airspeed but is only relevant above 200 knots.

Position Error

Position error occurs because of pitot-static system errors. Errors vary with speed and attitude and include maneuver-induced errors. Pressure error correction (PEC) is shown in the pilot’s operating handbook. Indicated airspeed corrected for pressure and instrument error is called calibrated airspeed (CAS).

Instrument Error

Instrument error is caused by small manufacturing imperfections and the large mechanical amplification necessary for small, sensed movements. Instrument error is insignificant in general aviation (GA) airplanes.

Altimeter

The altimeter converts static pressure at the level of the airplane to register vertical distance from a datum (the reference from which a measurement is made). At lower altitudes, a one inch decrease in pressure indicates approximately 1,000 feet gain in altitude. For all operations in the U.S. below 18,000 feet, the local altimeter setting is used. Since the height of terrain and obstacles shown on a chart is above mean sea level (MSL), this becomes your altitude reference. At or above 18,000 feet MSL, standard pressure (29.92 in. Hg) is set and flight levels are reported to the nearest 100 feet (e.g. 11,500 feet is FL115), although cruising levels are usually whole thousands of feet (e.g. FL120). For all operations below 18,000 feet (the transition altitude), pilots are required to use the current local altimeter setting and then set 29.92 in. Hg when climbing through 18,000 feet. The setting is changed from standard pressure to the local altimeter setting when descending through FL180 (the transition level).

Figure 1-3 Altimeter.

At or above 18,000 feet MSL, set 29.92 in. Hg in the pressure window. Below 18,000 feet MSL, set the local altimeter setting in the pressure window.

Altimeter Errors

Barometric Error

Barometric error is induced in an altimeter when atmospheric pressure at sea level differs from standard atmospheric conditions. The correct setting of the barometric subscale removes the error.

Temperature Error

Temperature error is induced when the temperature (density) differs from standard atmospheric conditions. Note that there is no adjustment.

Position Error

Position error occurs because of static system errors and is minor. Errors vary with speed and attitude and include maneuver-induced errors.

Instrument Error

Instrument error is caused by small manufacturing imperfections and is insignificant.

Lag

Lag occurs when the response of the capsule and linkage is not instantaneous. The altimeter reading lags slightly when altitude is increased or decreased rapidly.

Altimeter Check

Whenever an accurate local altimeter setting is available and the airplane is at an airfield with a known elevation, pilots must conduct an accuracy check of the altimeter before takeoff. The altimeter is checked by comparing its indicated altitude to a known elevation using an accurate local altimeter setting. The altimeter should indicate site elevation within 75 feet; if it doesn’t, have a mechanic inspect the altimeter prior to takeoff.

When operating out of a tower-controlled airport, you will have access to an accurate local altimeter setting; however, you may need to make an allowance for the difference between the airfield reference point and the position of your airplane at the time. Basically, a local altimeter setting that is provided by a tower, ATIS or remote-reporting airfield sensor can be considered accurate.

Vertical Speed Indicator

The vertical speed indicator (VSI) indicates the rate of change of altitude. The VSI is more sensitive to static pressure changes than the altimeter, and so it responds more quickly to an altitude change. However, there will always be some lag. Its principle of operation depends on lag. Generally, the trend is obvious almost immediately, but the precise rate will take a few seconds to be indicated. With large and sudden attitude changes, the VSI may briefly show a reversed reading before a steady rate of climb or descent is indicated because of disturbed airflow near the static vent. This is also likely in rough air. The lag can last as long as several seconds before the rate can be read—therefore fly attitude; be careful not to chase the VSI needle.

Figure 1-4 Vertical speed indicator (VSI).

Gyroscopic Instruments

Attitude Indicator

The attitude indicator (AI) is the only instrument that gives a direct and immediate picture of the pitch and bank of the airplane. You should become familiar with the specific attitudes you need to select and maintain for your airplane.

Figure 1-5 Pitch attitude.

Figure 1-6 Bank attitude.

Attitude Indicator Errors

The attitude indicator is a reliable and accurate instrument. However, it may be subject to failures of the gyroscope drive system and precession errors.

If the AI suffers a failure of its rotor drive, it will become unstable. An electrically driven AI will usually have a warning flag to alert you of a power failure. If a power failure occurs, the AI will be unreliable and provide false attitude information. A failure in a vacuum-driven AI will produce the same result. To guard against this, you must monitor the suction gauge at regular intervals to ensure that an adequate vacuum pressure of between 3 and 5 inches of Hg is being provided.

The AI suffers from errors during sustained accelerations and turns because the erection switch senses a false vertical. A linear acceleration will exert g-forces that affect the self-erecting mechanism of the AI. During a rapid acceleration, as can occur at takeoff, the gravity sensors on the bottom of the gyroscope tend to get left behind and cause the gyroscope to precess forward at the top, moving the horizon bar down slightly producing a false indication of a climb. It responds just like its pilot’s inner ear, and acceleration is sensed as a tilt (somatogravic illusion). These can cause false indications of pitch attitude and bank angle. The errors are usually small and are easily identified and corrected. Be careful immediately after a night takeoff to maintain a positive rate of climb.

Turn and Coordination Instruments

Coordination Ball/Inclinometer

If an airplane is not in coordinated flight, it will be either slipping or skidding. A curved glass tube filled with damping oil and containing a ball is provided to indicate slip or skid. It acts like a pendulum. The position of the ball is determined by the resultant of centrifugal reaction and gravity. The ball is not connected to the turn gyro.

Figure 1-7 Coordination ball.

Turn Indicator/Turn Coordinator

On a turn indicator, the pointer is calibrated to show standard-rate—or rate-one—turns, left or right. A standard-rate turn causes the heading to change at 3° per second, hence a complete turn of 360° will take 2 minutes. Note that the wings are pivoted in the center and do not move up or down to indicate changes in pitch attitude. To avoid confusion with the attitude indicator, many turn coordinators are labeled with the warning, no pitch information (figure 1-9).

Figure 1-8 Turn indicator.

Figure 1-9 Turn coordinator.

Heading Indicator

The heading indicator (HI), sometimes referred to as the directional gyro (DG), is a directional instrument, but it has no inherent magnetic alignment. It contains a gyroscope powered by either a vacuum system or the electrical system. It relies on the pilot to manually align it with the magnetic compass after start and regularly in flight.

Figure 1-10 Heading indicator.

Heading Indicator Errors

The gyroscope in the HI does drift and needs to be realigned periodically (every 15 minutes). In flight, the airplane must be straight and level and stabilized whenever the HI is being aligned.

Compass Instruments

Magnetic Compass

The magnetic compass, or direct indicating compass, is the fundamental heading reference. In steady flight, magnetic heading appears under the lubber line, which indicates the nose of the airplane. Small errors in the reading will occur because of the influence of additional magnetic fields generated by the airplane and its components. A cockpit placard, known as the deviation card or compass correction card (figure 1-12), enables the pilot to allow for these errors. The deviation is very small. In straight-and-level, unaccelerated flight, the compass is accurate.

Figure 1-11 
Magnetic compass.

Fiugre 1-12 
Deviation card (compass correction card).

The indications of the direct indicating compass are subject to significant errors when the airplane is turning (especially through north or south), and when accelerating (especially on east and west). These errors arise because of the adverse effect of magnetic dip, which is caused by the vertical component of the earth’s magnetic field. The indications can also be misread as the direction to turn appears in reverse.

Remote Indicating Compass

A remote indicating compass combines the functions of the magnetic compass and the heading indicator. It employs a magnetic sensor, called a flux valve or a magnetic flux detector, that is positioned well away from other magnetic influences in the airframe, usually in a wing tip.

The sensor detects the earth’s magnetic field and sends electrical signals to the gyro to automatically align it and therefore show the correct magnetic heading of the airplane. This process is known as slaving. It eliminates the need to manually realign the HI.

There is usually a small slaving knob on the instrument to allow the pilot to manually align the compass card quickly if the indicated heading is grossly in error. A small slaving annunciator is usually provided to assist manual alignment and allow the pilot to check that normal automatic slaving is occurring. This is indicated by small, regular oscillations of the slaving needle. Alignment is also cross-checked with the magnetic compass.

The gyro-stabilized magnetic compass is also used to drive the compass card in the radio magnetic indicator (RMI). Navigation information is superimposed on the heading indication (figure 1-13).

Figure 1-13 
Radiomagnetic indicator with heading bug at the top and two ADF needles.

The more modern horizontal situation indicator (HSI) also presents a gyro-stabilized magnetic heading on a rotating card (figure 1-14). This may be presented with other useful guidance information on a mechanical instrument or an electronic display as part of an electronic flight instrumentation system (EFIS).

Figure 1-14 
Horizontal situation indicator.

Other Instruments

Clock

One of the most important instruments for night operations is the clock, which is often placed on the control column. Make sure you are familiar with the functions of the clock, whether digital or analog, before going