Introduction
Changing weather conditions, air traffic control (ATC), the
aircraft, and the pilot are all variables that make instrument
flying an unpredictable and challenging operation. The safety
of the flight depends upon the pilot’s ability to manage these
variables while maintaining positive aircraft control and
adequate situational awareness. This chapter discusses the
recognition and suggested remedies for such abnormal and
emergency events related to unforecasted, adverse weather;
aircraft system malfunctions; communication/navigation
system malfunctions; and loss of situational awareness.
Emergency
Operations
Chapter 11
Unforecast Adverse Weather
Inadvertent Thunderstorm Encounter
A pilot should avoid flying through a thunderstorm of any
intensity. However, certain conditions may be present
that could lead to an inadvertent thunderstorm encounter.
For example, flying in areas where thunderstorms are
embedded in large cloud masses may make thunderstorm
avoidance difficult, even when the aircraft is equipped
with thunderstorm detection equipment. Therefore, pilots
must be prepared to deal with an inadvertent thunderstorm
penetration. At the very least, a thunderstorm encounter
subjects the aircraft to turbulence that could be severe. The
pilot and passengers should tighten seat belts and shoulder
harnesses, and secure any loose items in the cabin.
As with any emergency, the first order of business during
an inadvertent thunderstorm encounter must be to fly the
aircraft. The pilot workload is heavy; therefore, increased
concentration is necessary to maintain an instrument scan.
If a pilot inadvertently enters a thunderstorm, it is better to
maintain a course straight through the thunderstorm rather
than turning around. A straight course minimizes the amount
of time in the thunderstorm, and turning maneuvers only
increase structural stress on the aircraft.
Reduce power to a setting that maintains a speed at the
recommended turbulence penetration speed as described in the
Pilot’s Operating Handbook/Airplane Flight Manual (POH/
AFM), and try to minimize additional power adjustments.
Concentrate on maintaining a level attitude while allowing
airspeed and altitude to fluctuate. Similarly, if using the
autopilot, disengage the altitude hold and speed hold modes,
as they only increase the aircraft’s maneuvering—thereby
increasing structural stress.
During a thunderstorm encounter, the potential for icing
also exists. As soon as possible, turn on anti-icing/deicing
equipment and carburetor heat, if equipped. Icing can be
rapid at any altitude and may lead to power failure and/or
loss of airspeed indication.
Lightning is also present in a thunderstorm and can
temporarily blind a pilot. To reduce this risk, turn up flight
deck lights to the highest intensity, concentrate on the flight
instruments, and resist the urge to look outside.
Inadvertent Icing Encounter
Because icing is unpredictable in nature, pilots may find
themselves in icing conditions even though they have done
everything practicable to avoid it. In order to stay alert to this
possibility while operating in visible moisture, pilots should
monitor the outside air temperature (OAT).
The effects of ice on aircraft are cumulative—thrust is
reduced, drag increases, lift lessens, and weight increases.
The results are an increase in stall speed and a deterioration
of aircraft performance. In extreme cases, two to three inches
of ice can form on the leading edge of the airfoil in less than 5
minutes. It takes only 1⁄2 inch of ice to reduce the lifting power
of some aircraft by 50 percent and increases the frictional
drag by an equal percentage.
A pilot can expect icing when flying in visible precipitation,
such as rain or cloud droplets, and the temperature is
between +02 and –10° Celsius. When icing is detected, a
pilot should do one of two things, particularly if the aircraft
is not equipped with deicing equipment: leave the area of
precipitation or go to an altitude where the temperature is
above freezing. This “warmer” altitude may not always be
a lower altitude. Proper preflight action includes obtaining
information on the freezing level and the above-freezing
levels in precipitation areas.
If neither option is available, consider an immediate landing
at the nearest suitable airport. Even if the aircraft is equipped
with anti-icing/deicing equipment, it is not designed to allow
aircraft to operate indefinitely in icing conditions. Anti-
icing/deicing equipment gives a pilot more time to get out of
the icing conditions. Report icing to ATC and request new
routing or altitude. Be sure to report the type of aircraft, and
use the following terms when reporting icing to ATC:
1. Trace. Ice becomes perceptible. Rate of accumulation
is slightly greater than sublimation. Anti-icing/deicing
equipment is not utilized unless encountered for an
extended period of time (over 1 hour).
2. Light. The rate of accumulation may create a problem
if flight is prolonged in this environment (over 1
hour). Occasional use of anti-icing/deicing equipment
removes/prevents accumulation. It does not present a
problem if anti-icing/deicing equipment is used.
3. Moderate. The rate of accumulation is such that even
short encounters become potentially hazardous and
use of anti-icing/deicing equipment or flight diversion
is necessary.
4. Severe. The rate of accumulation is such that anti-
icing/deicing equipment fails to reduce or control the
hazard. Immediate flight diversion is necessary.
Early ice detection is critical and is particularly difficult during
night flight. Use a flashlight to check for ice accumulation on
the wings. At the first indication of ice accumulation, take
action to get out of the icing conditions. Refer to the POH/
AFM for the proper use of anti-icing/deicing equipment.
Figure 11-2. One example of a static wick installed on aircraft
control surface to bleed off static charges built up during flight.
Figure 11-2. One example of a static wick installed on aircraft
control surface to bleed off static charges built up during flight.
This prevents static buildup and St. Elmo’s fire by allowing the
static electricity to dissipate harmlessly.
Figure 11-1. St. Elmo’s Fire is harmless but may affect both communication and navigation radios, especially the lower frequencies
such as those used on the automatic direction finding (ADF).
Precipitation Static
Precipitation static, often referred to as P-static, occurs
when accumulated static electricity is discharged from the
extremities of the aircraft. This discharge has the potential
to create problems for the instrument pilot. These problems
range from the serious, such as erroneous magnetic compass
readings and the complete loss of very high frequency (VHF)
communications to the annoyance of high-pitched audio
squealing and St. Elmo’s fire. [Figure 11-1]
Precipitation static is caused when an aircraft encounters
airborne particles during flight (e.g., rain or snow) and
develops a negative charge. It can also result from
atmospheric electric fields in thunderstorm clouds. When
a significant negative voltage level is reached, the aircraft
discharges it, which can create electrical disturbances. This
electrical discharge builds with time as the aircraft flies in
precipitation. It is usually encountered in rain, but snow can
cause the same effect. As the static buildup increases, the
effectiveness of both communication and navigation systems
decreases to the point of potential unusability.
To reduce the problems associated with P-static, the pilot
should ensure the aircraft’s static wicks are properly maintained
and accounted for. Broken or missing static wicks should be
replaced before an instrument flight. [Figure 11-2]
Aircraft System Malfunctions
Preventing aircraft system malfunctions that might lead
to an inflight emergency begins with a thorough preflight
ALERTS
NA V1 108.00 113.00
NA V2 108.00 110.60
134.000 118.000 COM1
123.800 118.000 COM2
WPT _ _ _ _ _ _ DIS _ _ . _ NM DTK _ _ _° TRK 360°
MAP
NA V1 108.00 113.00
NA V2 108.00 110.60
134.000 118.000 COM1
123.800 118.000 COM2
GS 120KT XTK 0.07NM ETE 24:24 ESA 2800FT
ALERTS
NA V1 108.00 113.00
NA V2 108.00 110.60
134.000 118.000 COM1
123.800 118.000 COM2
WPT _ _ _ _ _ _ DIS _ _ . _ NM DTK _ _ _° TRK 360°
Figure 11-3. Illustrates the system (in this case the G1000) when the PFD display fails and it the reversionary mode is used.
DCLTR
Normal Mode
Display Failure / Reversionary Mode
MAP - NA VIGA TION MAP
Figure 11-3. G1000 PFD display in normal mode and in the reversionary mode activated upon system failure.
inspection. In addition to those items normally checked
prior to a visual flight rules (VFR) flight, pilots intending to
fly under instrument flight rules (IFR) should pay particular
attention to the alternator belt, antennas, static wicks, anti-
icing/deicing equipment, pitot tube, and static ports.
During taxi, verify the operation and accuracy of all flight
instruments. In addition, during the run-up, verify that the
operation of the pneumatic system(s) is within acceptable
parameters. It is critical that all systems are determined to be
operational before departing into IFR conditions.
Electronic Flight Display Malfunction
When a pilot becomes familiar and comfortable with the
new electronic displays, he or she also tends to become more
reliant on the system. The system then becomes a primary
source of navigation and data acquisition instead of the
supplementary source of data as initially intended.
Complete reliance on the moving map for navigation becomes
a problem during a failure of one, more, or all of the flight
display screens. Under these conditions, the systems revert to
a composite mode (called reversionary), which eliminates the
moving map display and combines the primary flight display
(PFD) with the engine indicating system. [Figure 11-3] If a
pilot has relied on the display for navigation information and
situational awareness, he or she lacks any concept of critical
data such as the aircraft’s position, the nearest airport, or
proximity to other aircraft.
The electronic flight display (EFD) is a supplementary source
of navigation data and does not replace en route charts.
To maintain situational awareness, a pilot must follow the
flight on the en route chart while monitoring the PFD. It is
important for the pilot to know the location of the closest
airport as well as surrounding traffic relative to the location
of his or her aircraft. This information becomes critical
should the EFD fail.
For the pilot who utilizes the electronic database as a
substitute for the Airport/Facilities Directory (A/FD), screen
failure or loss of electrical power can mean the pilot is no
longer able to access airport information. Once the pilot
loses the ability to call up airport information, aeronautical
decision-making (ADM) is compromised.
Figure 11-4. Ammeter (left) and loadmeter (right).
Figure 11-5. The double rocker switch. Figure 11-5. Double rocker switch seen on many aircraft.
IN.
Hg.
+ 60
- 60
AL T AMPS
0 30 60
Figure 11-4. Ammeter & Loadmeter.
Ammeter
Loadmeter
Alternator/Generator Failure
Depending upon the aircraft being flown, an alternator failure
is indicated in different ways. Some aircraft use an ammeter
that indicates the state of charge or discharge of the battery.
[Figure 11-4] A positive indication on the ammeter indicates
a charge condition; a negative indication reveals a discharge
condition. Other aircraft use a loadmeter to indicate the load
being carried by the alternator. [Figure 11-4]
Sometimes an indicator light is also installed in the aircraft to
alert the pilot to an alternator failure. On some aircraft, such
as the Cessna 172, the light is located on the lower left side
making it difficult to see its illumination if charts are open.
Ensure that these safety indicators are visible during flight.
When a loss of the electrical charging system is experienced,
the pilot has approximately 40 minutes of battery life
remaining before the system fails entirely. The time
mentioned is an approximation and should not be relied upon
as specific to all aircraft. In addition, the battery charge that
exists in a battery may not be full, altering the time available
before electrical exhaustion occurs. At no time should a pilot
consider continuing a flight once the electrical charging
system has failed. Land at the nearest suitable airport.
Techniques for Electrical Usage
Master Battery Switch
One technique for conserving the main battery charge is
to fly the aircraft to the airport of intended landing while
operating with minimal power. If a two-position battery
master/alternator rocker switch is installed, it can be utilized
to isolate the main battery from the electrical system and
conserve power. [Figure 11-5]
Operating on the Main Battery
While en route to the airport of intended landing, reduce the
electrical load as much as practical. Turn off all unnecessary
electrical items, such as duplicate radios, non-essential
lighting, etc. If unable to turn off radios, lights, etc., manually,
consider pulling circuit breakers to isolate those pieces of
equipment from the electrical system. Maximum time of
useful voltage may be between 30 and 40 minutes and is
influenced by many factors, that degrade the useful time.
Loss of Alternator/Generator for Electronic Flight
Instrumentation
With the increase in electrical components being installed
in modern technically advanced aircraft, the power supply
and the charging system need increased attention and
Figure 11-6. The standby battery must be armed to work
correctly and arming should be done prior to departure.
Double rocker switch
Figure 11-6. Note the double rocker switch and the standby battery
switch in this aircraft. The standby battery must be armed to work
correctly; arming should be done prior to departure.
understanding. Traditional round dial aircraft do not rely
as heavily on electrical power for the primary six-pack
instrumentation. Modern EFDs utilize the electrical system
to power the Attitude Heading Reference System (AHRS),
air data computer (ADC), engine indicating system (EIS),
etc. A loss of an alternator or generator was considered an
abnormality in traditionally-equipped aircraft; however,
a failure of this magnitude is considered an emergency in
technically advanced aircraft.
Due to the increased demand for electrical power, it is
necessary for manufacturers to install a standby battery in
conjunction with the primary battery. The standby battery is
held in reserve and kept charged in case of a failure of the
charging system and a subsequent exhaustion of the main
battery. The standby battery is brought online when the main
battery voltage is depleted to a specific value, approximately
19 volts. Generally, the standby battery switch must be in
the ARM position for this to occur but pilots should refer to
the aircraft flight manual (AFM) for specifics on an aircraft’s
electrical system. The standby battery powers the essential
bus and allows the PFD to be utilized.
The essential bus usually powers the following components:
1. AHRS (Attitude and Heading Reference System)
2. ADC (Air Data Computer)
3. PFD (Primary Flight Display)
4. Navigation Radio #1
5. Communication Radio #1
6. Standby Indicator Light
Techniques for Electrical Usage
Standby Battery
One technique for conserving the main battery charge is to
fly the aircraft to the airport of intended landing while using
the standby battery. A two-position battery master/ alternator
rocker switch is installed on most aircraft with EFDs, which
can be utilized to isolate the main battery from the electrical
system. By switching the MASTER side off, the battery is
taken offline and the standby battery comes online to power the
essential bus. However, the standby battery switch must be in
the ARM position for this to occur. [Figure 11-6] Utilization
of the standby battery first reserves the main battery for use
when approaching to land. With this technique, electrical
power may be available for the use of flaps, gear, lights, etc. Do
not rely on any power to be available after the standby battery
has exhausted itself. Once the charging system has failed,
flight with a powered electrical system is not guaranteed.
Operating on the Main Battery
While en route to the airport of intended landing, reduce the
electrical load as much as practical. Turn off all unnecessary
electrical items, such as duplicate radios, non-essential
lighting, etc. If unable to turn off radios, lights, etc., manually,
consider pulling circuit breakers to isolate those pieces of
equipment from the electrical system. Keep in mind that
once the standby battery has exhausted its charge, the flight
deck may become very dark depending on what time of
day the failure occurs. The priority during this emergency
situation is landing the aircraft as soon as possible without
jeopardizing safety.
A standby attitude indicator, altimeter, airspeed indicator (ASI)
and magnetic compass are installed in each aircraft for use
when the PFD instrumentation is unavailable. [Figure 11-7]
These would be the only instruments left available to the pilot.
Navigation would be limited to pilotage and dead reckoning
unless a hand-held transceiver with a global positioning
system (GPS)/navigation function is onboard.
Once an alternator failure has been detected, the pilot must
reduce the electrical load on the battery and land as soon as
practical. Depending upon the electrical load and condition
of the battery, there may be sufficient power available for
45 minutes of flight—or for only a matter of minutes. Pilots
should also know which systems on the aircraft are electric and
ALERTS
NA V1 108.00 113.00
NA V2 108.00 110.60
134.000 118.000 COM1
123.800 118.000 COM2
WPT _ _ _ _ _ _ DIS _ _ . _ NM DTK _ _ _° TRK 360°
N-S
E-W
Figure 11-7. The stand-by instrumentation available to the pilot on Electronic Flight Instrumented Aircraft. Figure 11-7. Emergency instrumentation available to the pilot on electronic flight instrumented aircraft.
those that continue to operate without electrical power. Pilots
can attempt to troubleshoot alternator failure by following the
established alternator failure procedure published in the POH/
AFM. If the alternator cannot be reset, advise ATC of the
situation and inform them of the impending electrical failure.
Analog Instrument Failure
A warning indicator, or an inconsistency between indications
on the attitude indicator and the supporting performance
instruments, usually identifies system or instrument failure.
Aircraft control must be maintained while identifying the
failed component(s). Expedite the cross-check and include
all flight instruments. The problem may be individual
instrument failure or a system failure affecting multiple
instruments.
One method of identification involves an immediate
comparison of the attitude indicator with the rate-of-turn
indicator and vertical speed indicator (VSI). Along with
providing pitch-and-bank information, this technique
compares the static system with the suction or pressure system
and the electrical system. Identify the failed component(s)
and use the remaining functional instruments to maintain
aircraft control.
Attempt to restore the inoperative component(s) by checking
the appropriate power source, changing to a backup or
alternate system, and resetting the instrument if possible.
Covering the failed instrument(s) may enhance a pilot’s
ability to maintain aircraft control and navigate the aircraft.
Usually, the next step is to advise ATC of the problem and,
if necessary, declare an emergency before the situation
deteriorates beyond the pilot’s ability to recover.
Pneumatic System Failure
One possible cause of instrument failure is a loss of the
suction or pressure source. This pressure or suction is
supplied by a vacuum pump mechanically driven off the
engine. Occasionally these pumps fail, leaving the pilot with
inoperative attitude and heading indicators.
Figure 11-8 illustrates inoperative vacuum driven attitude
and heading indicators that can fail progressively. As the
gyroscopes slow down, they may wander, which, if connected
to the autopilot and/or flight director, can cause incorrect
movement or erroneous indications. In Figure 11-8, the
aircraft is actually level and at 2,000 feet mean sea level
(MSL). It is not in a turn to the left which the pilot may
misinterpret if he or she fails to see the off or failed flags.
If that occurs, the pilot may transform a normally benign
situation into a hazardous situation. Again, good decision-
making by the pilot only occurs after a careful analysis of
systems.
Many small aircraft are not equipped with a warning system
for vacuum failure; therefore, the pilot should monitor the
30.0 29.9 29.8
Figure 11-8. Vacuum failure - inoperative attitude and heading indicators. Figure 11-8. Vacuum failure.
system’s vacuum/pressure gauge. This can be a hazardous
situation with the potential to lead the unsuspecting pilot into
a dangerous unusual attitude that would require a partial panel
recovery. It is important that pilots practice instrument flight
without reference to the attitude and heading indicators in
preparation for such a failure.
Pitot/Static System Failure
A pitot or static system failure can also cause erratic and
unreliable instrument indications. When a static system
problem occurs, it affects the ASI, altimeter, and the VSI.
In most aircraft, provisions have been made for the pilot to
select an alternate static source. Check the POH/AFM for
the location and operation of the alternate static source. In
the absence of an alternate static source, in an unpressurized
aircraft, the pilot could break the glass on the VSI. The VSI
is not required for instrument flight, and breaking the glass
provides the altimeter and the ASI a source of static pressure.
This procedure could cause additional instrument errors.
Communication/Navigation System
Malfunction
Avionics equipment has become very reliable, and the
likelihood of a complete communications failure is remote.
However, each IFR flight should be planned and executed in
anticipation of a two-way radio failure. At any given point
during a flight, the pilot must know exactly what route to fly,
what altitude to fly, and when to continue beyond a clearance
limit. Title 14 of the Code of Federal Regulations (14 CFR)
part 91 describes the procedures to be followed in case of a
two-way radio communications failure. If operating in VFR
conditions at the time of the failure, the pilot should continue
the flight under VFR and land as soon as practicable. If the
failure occurs in IFR conditions, or if VFR conditions cannot
be maintained, the pilot must continue the flight:
1. Along the route assigned in the last ATC clearance
received;
2. If being radar vectored, by the direct route from the
point of radio failure to the fix, route, or airway specified
in the vector clearance;
3. In the absence of an assigned route, by the route
that ATC has advised may be expected in a further
clearance; or
4. In the absence of an assigned route or a route that ATC
has advised may be expected in a further clearance,
by the route filed in the flight plan.
The pilot should maintain the highest of the following
altitudes or flight levels for the route segment being flown:
1. The altitude or flight level assigned in the last ATC
clearance received;
2. The minimum altitude (converted, if appropriate, to
minimum flight level as prescribed in 14 CFR, part
91 for IFR operations); or
3. The altitude or flight level ATC has advised may be
expected in a further clearance.
In addition to route and altitude, the pilot must also plan the
progress of the flight to leave the clearance limit.