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Tech Questions (Part 2)

This is part 2 of our technical question study guide. Remember to verify the accuracy of all the answers given below from another source, as the information may be out of date or even in error. The list is by no means exhaustive, but it should give you a general idea of the technical knowledge you need to have.

Questions

What is the difference between wet and damp runway?

Damp: The surface shows a change of colour due to moisture

Wet: The surface is soaked but there is not standing water

Wet patches: Patches of standing water are visible

Flooded: Extensive standing water is visible

Is the wind reported as true or magnetic in a TAF?

True

Is the wind reported as true or magnetic in an ATIS?

Magnetic

What does it mean if you see alternating white and red lights on the RWY?

If it’s a British Calvert Lighting design you have 3000' of runway remaining, and if its US ASLF design it's the last 2000'. Go on the safe side and assume its 2000'

How do you know you are out of the critical area after a low visibility landing?

Taxiway holding point markings (boxed line)

What happens to profile and induced drag with speed?

Profile increases (squared)

Induced decreases

What is max range with respect to drag curve?

1.32 Vimd

Critical engine on a 4 engined aircraft?

Upwind engine

At 33,000', when do you start descending?

3:1 descent = 99nm

What if you're heavy, what if you have to keep a lower speed in descent?

Still a 3:1 decent, just vary RoD

Heavier, requires a higher RoD

Slower speed, requires a lower RoD

When does holdover time start?

It starts at the beginning of the 1st anti-ice/de-ice application if only one application or at the beginning of the 2nd application when two applications are required.

Doing the turnaround, you find a nose gear door missing, what would you do?

Check MEL/CDL (Configuration Deviation List)

What is the tropopause, its temperature, and altitude?

It is the region at the top of the troposphere where a temperature inversion exists i.e. the temperature is isothermal. It's is variable in height, though the standard atmosphere assumes it to be at 36 000' and isothermic at -57ºc

What is the windshear procedure on the Metro?

Simultaneously

• Apply max power
• Ensure wings level
• Up to 18º pitch (until stick shaker)
• Don't reconfigure or increase airspeed until terrain clearance is assured

What happens when you pull the fire handle on the Metro?

A detonator fires and 1.1kg of Halon 1301 is discharged by a 500-800 psi nitrogen. It is a single use system with only bottle to respective engine capability.

The last flap setting on the 747 creates a lot of drag, why?

You are creating a lot of lift and consequently a lot of drag, this has several beneficial effects, it allows lower Vref speeds and less landing distance and the ability to spool up to high approach idle on final.

Larger flap setting, how does it affect take-off roll, screen height?

Larger flap settings will decrease the landing roll but reduce the climb gradient

Climbing at constant MN, what happens to IAS, TAS?

IAS decreases

TAS decreases

Tell us about the Metro's engines (type, SHP)

TPE-331-12UAR

1100shp

How many compressor/turbine stages?

2 centrifugal compressors

3 axial flow turbines

What is the cargo compartment max loading on the Metro?

Nose - 333kg

Zone A - 227

Zone B - 272

What happens when you start the engine with on the GPU with not enough voltage?

A hung start possibly leading to a hot start

What’s a hung start? What’s a hot start? When and why do we have them?

A potential hot start is indicated by an abnormally rapid EGT rise after light off. By monitoring fuel flow and EGT, a hot start can be anticipated before the 770ºc limit is exceeded.

Hot Starts may be caused by ...

• Inadequate starter voltage, resulting in insufficient compressor airflow.
• Premature starter deactivation
• Incomplete purging of fuel in the combustion chamber from the previous start attempt.
• Foreign object damage preventing sufficient engine acceleration and airflow.
• Incorrect start fuel scheduling.

How to identify a hung start?

A hung start is identified by light off followed by abnormally slow acceleration. A hung start may be result of fuel scheduling being either too lean or too rich. A lean hung start is associated with low fuel flow and proportionally low EGT. A rich condition can be recognized by a high fuel flow and an EGT rise, which may tend to develop into an over-temperature condition and possible compressor stall.

Hung Starts may be caused by...

• Starter air pressure too low to accelerate engine to self-sustaining speed
• Premature starter deactivation
• FOD to compressor
• Turbine section damage.

What is the hazard of using the BCF fire extinguisher in the cockpit?

Asphyxiation if you're not on oxygen

Why are V1 and VR significantly different on the 747-400?

Due to the large take-off weight

How do you find and determine V1 and Vr?

What do you do on the wet runway with V1?

V1 may be reduced (usually by a maximum of 10kts), due to the reduced stopping ability, in doing so the aircraft my not reach the 35' screen height because of the longer acceleration with OEI, so the screen height may now be reduced to 15'.

What is Vmcg?

Minimum control speed, ground.

Can V1 be less than Vmcg? Can it be equal?

No

Yes

Where is the critical engine on the Metro and why?

The number 2 engine

Due to Asymmetric blade effect and Propeller slipstream

Does the 747-400 have critical engines?

Yes

In a crosswind, which engine the most critical?

The outboard, upwind engine (increased yaw)

Where are the high lift devices located on the 747-400 and what type are they?

How many slots on the 747-400’s fowler flap?

3

Why is the 747-400 fowler flap fully extended (nearly perpendicular to the wing) on very short final?

To produce maximum lift and drag, reducing the approach speed and allowing the engines to be at high approach idle

What is the difference between max range and max endurance (definition).

Max range is the most distance for a given amount of fuel, it equates to 1.32 Vimd at a constant airspeed

Max endurance is the most time you can stay in the air, it equates to minimum power, and corresponds to the minimum lift/drag ration and is a fixed AoA.

What happens to Mach number when you climb at constant IAS. Why?

Mach number and TAS increase

Relationship to the local speed of sound as temperature decreases

How would you load the 747-400 to obtain max range? Why?

With the most rearward C of G practicable, to reduce the down force required on the elevator, thus reducing drag.

How many feet in 1hpa? Is it always constant with altitude?

30'

No

At 33,000 ft the OAT is -45C, what is ISA deviation?

ISA -06ºc

What height should you be at 15nm on slope on the ILS?  

4500'

If your IAS is 150kts on slope and established on the ILS and your VSI reads 1200fpm, what’s happening?

You will start descending below the glide slope

Explain the fohn wind. Where do you find fohn wind in Australia?

The Fohn is due to a mountain barrier. The classic Fohn wind experienced in the Alps is caused by air-cooling as it rises over the mountains, with moisture lost as precipitation. On the other side of the mountain the air sinks and is warmed by adiabatic compression as it descends.

What is Epsilon and dither?

They are two errors that can be intentionally imposed on the GPS system, otherwise known as Selective availability (S/A).

Dither is manipulation of the satellite clock information in the signal.

Epsilon is manipulating navigation message, orbit data.

What are some aerodynamic qualities associated with operating at high altitudes?

Less aerodynamic damping

Restricted operating range (Buffet boundaries)

Reduced manoeuvring ability

Why do jets operate at high altitudes?

To make coincident the best operating conditions for the airframe and engines.

Airframe: The higher the altitude the higher the TAS for a given EAS and drag, therefore more air miles are covered for the fuel used to produce the thrust, equal to drag.

Engines: Best TSFC occurs typically at around 90% engine RPM. Since thrust falls with altitude, it follows that only at high altitude will the thrust be low enough to equal the required thrust at normal cruise RPM.

Shockwaves and compressibility

As flight speed nears the speed of sound, a compression wave will form at the leading edge and all changes in velocity and pressure will take place quite sharply and suddenly.

The principle difference between subsonic and supersonic flow is due to the compressibility of the supersonic flow.

Describe Normal Shockwaves

Whenever the shockwave forms perpendicular to the upstream flow, the shockwave is termed a Normal shockwave and the flow immediately behind the shockwave is subsonic. Whenever a supersonic airstream is slowed to subsonic without a change in direction, a normal shockwave will form as a boundary between the supersonic and subsonic regions.

Supersonic airstream passing through a normal shockwave will experience the following changes:

• The airstream is slowed to subsonic. The local Mach number behind the shockwave is roughly equal to the reciprocal of the Mach number ahead of the shockwave. (M1.25/M0.80)
• The airflow direction immediately behind the wave unchanged
• The static pressure of the airstream behind the wave is greatly increased
• The density of the airstream (as indicated by total pressure) is greatly reduced. The normal shockwave is very wasteful of energy

Shockwaves cause:

• Increased drag
• Reduced lift
• Nose down pitching tendency  

See also

Tech Questions

Categories: Airline Interviews | Questions