Technical Interview 8 Flashcards
What is the height of the tropopause according to ISA?
36,090ft in ISA
Are jet streams there all year round?
There are 2 permanent jet streams that exist all year around although their average position changes with the seasons:
Polar Front jet (westerly): occurs as a result of the temperature gradient along the Polar Front (boundary between Polar and Tropical air masses),
Sub-Tropical jet (westerly): occurs as a result of Hadley and Farrel cell circulation = in the sub-tropical high pressure belt.
There are also 2 other major jet streams of a seasonal character:
Arctic jet (westerly): occurs in the winter months, typically around 60°N, in a boundary between the arctic and polar air masses,
Equatorial jet (easterly): occurs during summer months around 15°N and blowing from SE Asia => S India => central Africa.
Is the tropopause uniform in height? If not, what height is it at the pole and the equator?
No, tropopause at the pole is lower (30.000ft) than at the equator (56.000ft)
What is the environmental lapse rate according to ISA?
1.98°C per 1000 ft increasing altitude
What is the average temperature at 25,000ft according to ISA?
-35°C
Which flight will take the shortest time, from London to New York or New York to London?
New York to London (flying east) would take less time because of the Polar front westerly jet stream.
What weather is associated with windshear?
CAT
Frontal passage
Microburst
What is the speed of sound at sea level according to ISA?
662 kts
Local speed of sound = 39 x √(Temperature in Kelvin)
15°C in Kelvin is (15 + 273) = 288
So the local speed of sound = 39 x √288 = 662 kts
Why don’t you want to fly your Seneca into a thunderstorm?
Note: question was asked to a candidate with previous Seneca experience
Severe turbulence can occur in, and around, any cumulonimbus clouds, and particularly around thunderstorms. The violent up and downdraughts within cumulonimbus are especially hazardous.
Severe icing may occur in cumulonimbus at temperatures between 0ºC and -45ºC. High concentrations of large, supercooled water droplets can lead to severe, clear icing accumulating on the airframe very quickly.
Hail may be encountered at any height in, and underneath, a thunderstorm. Hail can also be experienced beneath the anvil of a cumulonimbus, outside the cloud. Severe damage to the skin of an airframe may be caused by hail.
Lightning within the vicinity of an aircraft can cause the following effects: temporary blindness, erroneous compass reading, skin damage to an aircraft struck by lightning.
Large and rapid pressure variations can occur in, and around cumulonimbus, which may lead to errors in indicated altitude of up to plus or minus 1 000 feet.
What are the problems associated with icing?
Aerodynamic. Ice tends to form on leading edges, thereby spoiling the aerodynamic shape . The result is reduced lift, increased drag, increased weight, increased stalling speed and increased fuel consumption.
Ice, frost or snow of a thickness and roughness similar to coarse sandpaper can reduce lift by 30% and increase drag by 40%
It is also possible for pieces of ice to break off other surfaces and to jam between the control surfaces and wings and tail
Weight. In severe conditions, ice can form at a rate of 1 inch in 2 minutes
There will be a loss of stability due to the weight of ice not being uniform across the airframe
This can lead to a displaced C of G . Similar uneven weight of ice on propeller blades can cause severe engine vibration
Ice breaking off propellers can cause skin damage
Instrument effects. Ice can block pressure heads and the readings of ASIs, VSI, altimeters and mach meters can be in error as a result
General. Windscreens and canopies can be obscured
A thin film of ice/frost can cause skin friction
Ice in landing gear wells can affect retraction
Ice on aerials can cause static interference
What is windshear?
Windshear is a sudden change in wind speed and/or direction that occurs over a short distance at any altitude in a vertical and/or horizontal plane. It can subject an aircraft to sudden updraughts, downdraughts, or extreme horizontal wind components, causing sudden loss of lift or violent changes in vertical speeds or altitudes. Windshear will cause abrupt displacement from the flight path and require substantial control action to counteract it.
A windshear encounter is a very dynamic event which can strike suddenly and with devastating effect which has been beyond the recovery powers of experienced pilots flying modern and powerful aircraft. An encounter may cause alarm, a damaged undercarriage, or a total catastrophe. The first and most vital defence is avoidance.
The most powerful examples of windshear are associated with thunderstorms (cumulonimbus clouds), but windshear can also be experienced in association with other meteorological features such as the passage of a front, or a marked low-level temperature inversion. The meteorological features of windshear will be dealt with fully elsewhere.
Tell me, I was looking out the window and I saw white strokes coming out of the engines at cruising level, but I didn’t see it from an aircraft taking off, why is that and what is the difference?
Those are contrails.
The jet engine exhaust gases consist of carbon dioxide and water vapour.
At high altitudes the wator vapour gets released in a very cold environment. This can cause the air to be saturated with water vapour and then condenses. If cold enough the condense can freeze into white droplets. This forms the contrails.
You are flying at FL350 and the temperature reads -30°C, is the aircraft at its optimum temperature?
No because it is warmer, according to ISA temperature should be -55°C
How are contrails formed?
Their formation is most often triggered by freezing water vapour from the exhaust of aircraft engines.
What are the dangers of flying into thunderstorms?
Severe turbulence can occur in, and around, any cumulonimbus clouds, and particularly around thunderstorms. The violent up and downdraughts within cumulonimbus are especially hazardous.
Severe icing may occur in cumulonimbus at temperatures between 0ºC and -45ºC. High concentrations of large, supercooled water droplets can lead to severe, clear icing accumulating on the airframe very quickly.
Hail may be encountered at any height in, and underneath, a thunderstorm. Hail can also be experienced beneath the anvil of a cumulonimbus, outside the cloud. Severe damage to the skin of an airframe may be caused by hail.
Lightning within the vicinity of an aircraft can cause the following effects: temporary blindness, erroneous compass reading, skin damage to an aircraft struck by lightning.
Large and rapid pressure variations can occur in, and around cumulonimbus, which may lead to errors in indicated altitude of up to plus or minus 1 000 feet.
