FRA Locomotive Engineer Certification (FLEC)

Correct: The Critical Mach Number is defined as the lowest flight Mach number at which the airflow over any part of the aircraft reaches the local speed of sound (Mach 1.0). At this point, supersonic flow begins to develop on the upper surface of the wing, leading to the formation of shock waves, which causes an increase in drag and potential changes in flight characteristics.

Incorrect: The idea that indicated and true airspeed become identical at high altitudes is incorrect because true airspeed continues to increase relative to indicated airspeed as air density decreases. Focusing on a decrease in total pressure at the stagnation point due to atmospheric thinning misidentifies the cause of transonic drag, which is actually related to wave formation rather than simple pressure loss. The strategy of assuming the boundary layer becomes entirely laminar at high speeds is aerodynamically unsound, as higher speeds and Reynolds numbers generally promote turbulent flow and increased skin friction rather than eliminating it.

Takeaway: Critical Mach Number marks the onset of transonic flow where local air velocity first reaches the speed of sound on the airframe.

Correct: A severe internal mechanical failure involves structural damage that disrupts the aerodynamic flow through the engine and increases internal friction. This results in an immediate loss of thrust (indicated by EPR and N1) and a rapid rise in EGT because the fuel-to-air ratio becomes excessively rich or mechanical components are grinding. The physical imbalance of damaged rotating assemblies typically produces significant airframe vibration.

Incorrect: Relying on a steady decline in fuel flow and N2 with decreasing EGT describes a flameout where combustion has ceased but the engine remains mechanically intact. The strategy of identifying erratic fluctuations that stabilize at idle is more indicative of a compressor stall or surge rather than structural failure. Focusing only on oil pressure and temperature changes suggests a lubrication system failure or leak which does not immediately signify the structural destruction of the engine core.

Takeaway: Severe internal engine failure is distinguished from a flameout by simultaneous thrust loss, excessive heat, and mechanical vibration.

Correct: Electrical bonding jumpers are critical for ensuring that all components of the aircraft airframe are at the same electrical potential. By maintaining a low-impedance path across joints and hinges, the airframe functions as a continuous conductive shell, often referred to as a Faraday cage. This shell reflects or absorbs external electromagnetic radiation, such as HIRF or lightning, preventing these currents from penetrating the interior and interfering with sensitive electronic flight systems.

Incorrect: The strategy of increasing resistance between moving parts is incorrect because high resistance would lead to potential differences and static accumulation, which actually increases the risk of EMI and spark discharge. Suggesting that jumpers act as sacrificial anodes for radiation confuses electrochemical corrosion protection with electromagnetic shielding principles. Opting to isolate the digital ground from the airframe is a flawed approach in aviation design, as a unified ground plane is necessary to provide a stable reference and to facilitate the shielding of signal wires against induced currents.

Takeaway: Proper electrical bonding ensures the airframe provides a continuous conductive shield that protects internal avionics from external electromagnetic interference and HIRF impacts.

Correct: Shock waves in the transonic range lead to flow separation. This separation prevents the control surface from effectively altering the pressure distribution on the wing or tail, thereby reducing the control moment.

Incorrect: Attributing the loss of control to excessive hinge moments focuses on mechanical or hydraulic limitations rather than the aerodynamic behavior of the airflow. Focusing only on air density fails to account for the specific compressibility effects that occur as the aircraft approaches the speed of sound. The strategy of blaming the shift in the aerodynamic center confuses changes in longitudinal stability with the actual aerodynamic efficiency of the control surface itself.

Takeaway: Transonic control effectiveness is primarily reduced by shock-induced flow separation that disrupts the pressure distribution over control surfaces.

Correct: A radar shadow occurs when a storm cell is so dense with precipitation that it absorbs or scatters the radar energy, preventing the beam from reaching and returning from objects behind it. This phenomenon, known as attenuation, means the radar cannot ‘see’ what is behind the primary cell. FAA guidance and standard operating procedures dictate that these areas must be avoided because they often mask even more intense convective activity or severe turbulence.

Incorrect: Interpreting the lack of returns as a clear corridor is a dangerous misconception that ignores the physical reality of radar attenuation in heavy precipitation. Relying on tilting the radar upward to look over the shadow is insufficient because convective activity and associated turbulence often extend well above the visible moisture or the radar’s effective scanning range. Choosing to increase the gain setting will not resolve the issue of total attenuation and may instead clutter the display with ground returns or noise without revealing the masked weather.

Takeaway: Radar shadows indicate severe attenuation and must be treated as areas of hidden, potentially extreme weather that require wide circumnavigation.

Correct: At higher density altitudes, such as those found at high-elevation airports or in high-temperature conditions, a specific indicated airspeed (IAS) corresponds to a higher true airspeed (TAS). Because the kinetic energy of the aircraft and the resulting groundspeed are tied to TAS (assuming constant wind), the aircraft will touch down faster relative to the ground than it would at sea level. This higher groundspeed directly results in a longer landing roll and increased total landing distance.

Incorrect: The strategy of increasing indicated airspeed to compensate for thin air is unnecessary because the aerodynamic stall occurs at approximately the same indicated airspeed regardless of altitude. Focusing only on a decrease in descent rate is incorrect; in fact, a higher groundspeed on a fixed glide path requires a higher vertical rate of descent to remain on the glideslope. Choosing to believe that aerodynamic braking effectiveness increases enough to neutralize groundspeed is a misconception, as the lower air density actually reduces the mass flow over surfaces, often decreasing the overall effectiveness of aerodynamic deceleration compared to sea level.

Takeaway: Higher density altitude increases true airspeed for a given indicated airspeed, resulting in higher groundspeeds and longer required landing distances.

Correct: Retarded ignition timing means the spark occurs closer to Top Dead Center than intended. This reduces the time available for the fuel-air mixture to burn and expand, resulting in lower peak cylinder pressure and a corresponding loss of engine power, which manifests as a higher than normal RPM drop while the engine remains smooth.

Correct: In the standard atmosphere, the troposphere is characterized by a steady decrease in temperature with altitude. Once the aircraft crosses the tropopause into the stratosphere, this lapse rate changes; the temperature remains constant or may even increase slightly with altitude. Furthermore, the stratosphere is known for being extremely dry, containing very little water vapor compared to the troposphere.

Incorrect: The idea that atmospheric pressure increases with altitude is physically incorrect as pressure always decreases as one moves away from the Earth’s surface. Suggesting that the chemical composition of the air changes significantly is a misconception; the ratio of nitrogen to oxygen remains nearly constant throughout the homosphere. The strategy of assuming the speed of sound increases in thinner air is flawed because the speed of sound is primarily dependent on temperature, and it actually decreases as the air gets colder at higher altitudes.

Takeaway: Entering the stratosphere is characterized by a stabilized temperature lapse rate and a significant reduction in atmospheric moisture content.

Correct: In the United States, Mode C transponders are required to transmit pressure altitude referenced to the standard datum of 29.92 inches Hg. This ensures that all aircraft are reporting altitude based on a consistent reference, which the ATC ground equipment then adjusts using the local altimeter setting to provide the controller with an accurate indicated altitude.

Correct: An aft Center of Gravity (CG) reduces the static margin, which is the distance between the CG and the neutral point, leading to decreased longitudinal stability. Because the CG is closer to the center of pressure, the horizontal stabilizer is required to produce less downward lift (tail-down force) to maintain level flight. This reduction in tail-down force means the main wing does not have to overcome as much downward pressure, resulting in a lower total lift requirement and a lower stall speed.

Incorrect: The assumption that stability increases with an aft CG is incorrect because stability is derived from the longitudinal arm between the CG and the tail; shortening this arm reduces the aircraft’s natural tendency to return to equilibrium. Suggesting that higher elevator control forces are required is inaccurate, as an aft CG typically results in lighter, more sensitive pitch control forces. The strategy of linking aft CG to increased wing loading is flawed because aft loading actually reduces the effective wing load by minimizing the required balancing force from the horizontal stabilizer.

Takeaway: An aft CG position reduces longitudinal stability while decreasing stall speed due to the reduction in required tail-down force.

Correct: When a gauge indicates a total loss of pressure but the system continues to operate normally with a full reservoir, the most likely cause is an indication or sensor failure. The Flight Engineer should verify the electrical power to the transmitter via the circuit breaker and check the independent low-pressure warning light to confirm if a real pressure loss has occurred.

Correct: In the Northern Hemisphere, as an aircraft descends into the friction layer, the reduction in wind speed caused by surface friction weakens the Coriolis force. This allows the pressure gradient force to deflect the wind toward the center of low pressure, resulting in a counter-clockwise shift known as backing and a reduction in total wind speed.

Incorrect: Claiming the wind will veer and increase in velocity describes the atmospheric behavior during a climb rather than a descent. Suggesting the wind will veer while decreasing in velocity incorrectly identifies the direction of the shift relative to the forces at play. Expecting the wind to back while increasing in velocity is contradictory because the directional change is specifically triggered by the loss of velocity due to surface contact.

Takeaway: Descending into the friction layer causes Northern Hemisphere winds to back and slow down as friction reduces the Coriolis effect.

Correct: A hung start is characterized by the engine failing to accelerate to its proper idle RPM after the fuel has been introduced and ignited. This typically happens because the starter lacks sufficient torque or the fuel control unit is not providing the correct schedule for acceleration. Because the compressor is not spinning fast enough to provide adequate cooling airflow, the Exhaust Gas Temperature will continue to rise, necessitating an immediate shutdown to prevent thermal damage to the turbine section.

Incorrect: Attributing the condition to a hot start focuses on the temperature rise but ignores the failure of the RPM to reach idle, and attempting to modulate fuel is not a standard emergency procedure during the start phase. Suggesting a compressor stall misidentifies the phase of operation and incorrectly advises waiting, which risks exceeding thermal limits while the engine is in a stagnated state. Assuming a normal starter cutout delay ignores the critical symptom of stagnated RPM and rising temperature, while cycling ignition does not address the underlying lack of rotational acceleration required to reach self-sustaining speeds.

Takeaway: A hung start involves stagnated RPM below idle and rising temperatures, requiring an immediate termination of the start sequence to protect the engine.

Correct: High density altitude, caused by high elevation and high temperatures, means there are fewer air molecules available for both the engines and the wings. For the engines, this results in a lower mass flow of air and a corresponding decrease in maximum thrust. For the wings, the aircraft must travel at a higher true airspeed to achieve the same indicated airspeed and dynamic pressure required for lift-off. The combination of reduced thrust for acceleration and the need for a higher true airspeed inevitably results in a longer ground roll and a shallower climb path.

Incorrect: The strategy of assuming higher temperatures increase engine efficiency is incorrect because high ambient temperatures actually reduce the density of the air entering the compressor, which decreases the mass flow and thermal efficiency of the turbine. Relying on the idea that reduced drag compensates for thrust loss is a misconception; while parasite drag is lower in thinner air for a given true airspeed, the loss of engine performance and the need for higher speeds far outweigh any drag reduction during takeoff. Choosing to believe that lift is achieved at a lower true airspeed is aerodynamically unsound, as thinner air requires a higher true airspeed to maintain the same lift coefficient and indicated airspeed.

Takeaway: High density altitude degrades aircraft performance by reducing engine thrust and requiring higher true airspeeds for takeoff and climb.

Correct: Dutch roll is a dynamic instability where the aircraft’s lateral (dihedral) stability is more powerful than its directional (yaw) stability. In swept-wing aircraft, a yawing motion causes the advancing wing to become more perpendicular to the airflow, increasing lift and causing a roll. Because the directional stability is relatively weak, the nose takes longer to return to the centerline, resulting in the characteristic weaving motion that requires a yaw damper for suppression.

Incorrect: The strategy of identifying spiral divergence is incorrect because that condition leads to a tightening spiral dive when directional stability overpowers lateral stability, rather than an oscillation. Focusing on phugoid oscillation is misplaced as it describes a longitudinal pitch stability issue involving energy exchange rather than a lateral-directional coupling. Attributing the motion to high-speed buffet is inaccurate because buffet is a structural vibration caused by airflow separation at high Mach numbers rather than a rhythmic directional oscillation.

Takeaway: Dutch roll occurs in swept-wing aircraft when lateral stability outweighs directional stability, necessitating the use of yaw dampers.

Correct: Thermal anti-ice systems function on the principle of prevention, using bleed air or electrical resistance to keep the leading edges above freezing temperatures, which requires activation before ice can bond to the surface. In contrast, pneumatic de-icing boots are a reactive system; they use mechanical expansion to crack and shed ice that has already formed, often requiring a small amount of accumulation to prevent ‘ice bridging’ where the ice forms a shell over the inflated boot.

Incorrect: The strategy of keeping pneumatic boots constantly inflated is incorrect because it would significantly distort the airfoil’s aerodynamic properties and fail to shed ice. Relying on thermal anti-ice only during approach ignores the critical need for lift preservation during the cruise and climb phases. The idea that thermal systems allow ice to form before melting is a misconception of de-icing rather than anti-icing. Opting to run all systems continuously based solely on temperature without the presence of visible moisture ignores standard FAA operating procedures and causes unnecessary engine bleed air penalties.

Takeaway: Anti-icing systems prevent ice formation through heat, while de-icing systems remove existing ice through mechanical or thermal cycles.

Correct: Flight envelope protection systems are designed to prevent the aircraft from exiting the safe flight envelope. When an overspeed condition is sensed near Vmo/Mmo, the system provides an automated nose-up pitch input or increases the artificial feel forces (resistance) on the control column. This intervention ensures the aircraft does not exceed structural speed limits or encounter Mach tuck, even if the pilot continues to provide nose-down inputs.

Incorrect: The strategy of automatically deploying flight spoilers is incorrect because speed brake logic is typically separate from primary envelope protection and could cause secondary structural loads if deployed abruptly at high speeds. Choosing to transition to direct law is counterproductive as it removes the electronic protections exactly when they are needed most to prevent an overspeed. Focusing on an automated emergency descent describes a specific cabin pressure loss protocol rather than a standard aerodynamic envelope protection response to turbulence-induced overspeed.

Takeaway: Flight envelope protection systems provide automated pitch or force interventions to keep the aircraft within safe aerodynamic and structural speed limits.

Correct: High temperatures and high elevations result in a high density altitude, meaning the air is less dense. This reduction in density decreases the mass flow of air through the engines, which reduces thrust. Additionally, because lift is proportional to air density, the aircraft must achieve a higher true airspeed to generate the same amount of lift, which increases the required runway length and necessitates a lower takeoff weight.

Incorrect: The strategy of attributing performance loss to air viscosity is incorrect because viscosity changes have a negligible effect on takeoff performance compared to the significant impact of density changes. Focusing on a reduction in calibrated airspeed is a misconception; the required calibrated airspeed for lift remains relatively constant for a given weight, but the ground speed required to achieve that airspeed increases. Choosing to link temperature to center of pressure shifts is aerodynamically unsound, as the center of pressure is primarily a function of the angle of attack and airfoil shape rather than ambient temperature.

Takeaway: High density altitude negatively impacts performance by reducing engine thrust and requiring higher ground speeds to generate necessary lift.

Correct: The most severe Clear Air Turbulence is typically found on the polar side, or the side with lower pressure, of the jet stream core. This specific region experiences the highest rates of horizontal and vertical wind shear, which are the primary physical drivers of CAT in the upper atmosphere.

Incorrect: Simply monitoring the center of the jet core is insufficient because high velocity alone does not cause turbulence; rather, it is the rapid change in velocity over a short distance that creates the hazard. The strategy of focusing on the equatorial side is often misleading as the wind gradients there are generally weaker and more gradual than those on the polar side. Opting for altitudes significantly above the tropopause is incorrect because jet stream activity and its associated shear are concentrated near the tropopause break and the jet core itself.

Takeaway: Significant jet stream turbulence is most likely encountered on the polar side of the core where wind shear is greatest.

Correct: 14 CFR Part 25.1155 requires that propeller systems have a means to prevent the propeller from moving to a pitch lower than the flight idle position in flight. This prevents excessive drag and potential loss of control.

Incorrect: Choosing to allow the propeller to reach the reverse pitch position automatically during a flameout would create catastrophic drag and is strictly prohibited. The strategy of locking the pitch at the last known setting is insufficient because it does not account for the need to feather the propeller to reduce drag. Opting for manual adjustment of governor oil pressure by the Flight Engineer is incorrect because constant-speed propellers are designed to be governed automatically to ensure engine protection.

Takeaway: FAA regulations mandate that propeller systems include safeguards to prevent the blades from moving below the flight idle pitch during flight.