High Altitude Operations Flashcards
High altitude operations allow for…
lower fuel consumption and avoidance of weather
oxygen mask prevent? but don’t help with?
prevent hypoxia but do not help with sinus and ear blocks or decompression sickness
pressurized air is generally obtained from…
from an aircrafts turbocharger or compressor section of turbine aircraft
pressurized air piston powered aircraft may use…
air supplied from each engine turbocharger through a sonic Venturi
pressurized air gas turbine powered aircraft
use air supplied from the compressor stage of the engine which is conditioned for the cabin
cabin pressurized system typically…
typically maintains a cabin pressure altitude of 8,000’
pressurization
prevents rapid changes of cabin altitude, pressure inside body exceeds that outside the body causing bloating, lower cabin altitudes reduce this effect but are only available to aircraft manufactured to withstand the stress
pressurization system permits
a reasonably fast exchange of air from the inside to the outside of the cabin to eliminate odors and remove stale air
aircraft altitude
actual height above sea level
ambient temperature
temperature in area immediately surrounding the aircraft
ambient pressure
pressure in area immediately surrounding aircraft
cabin altitude
cabin pressure in terms of equivalent altitude above sea level
differential pressure
difference in pressure between the pressure acting on one side of a wall and the pressure acting on the other side of the wall. In aircraft air-conditioning and pressurizing systems, it is the difference between cabin pressure and atmospheric pressure
cabin pressure control system provides
cabin pressure regulation, pressure relief, vacuum relief, and the means for selecting the desired cabin altitude in the isobaric and differential range
dumping of cabin pressure
what is used to accomplish functions of cabin pressure control system
cabin pressure regulator, outflow valve, and a safety valve
cabin pressure regulator controls
cabin pressure to a selected value in the isobaric range and limits cabin pressure to a preset differential value in the differential range
differential control is used
to prevent the maximum differential pressure, from which the fuselage was designed, from being exceeded
cabin air pressure safety valve is
a combination pressure relief, vacuum relief, and dump valve
the pressure relieve valve prevents
cabin pressure from exceeding a predetermined differential pressure above ambient pressure
vacuum relief prevents..
ambient pressure from exceeding cabin pressure by allowing external air to enter the cabin when ambient pressure exceeds cabin pressure
dump valve
flight deck controls switch actuates it
when placed to ram a solenoid valve opens, causing the valve to dump cabin air to satmosphere
what limits degree of pressurization and the operating altitude of the aircraft
fuselage design to withstand a particular max cabin differential pressure
cabin differential pressure gauge
difference between inside and outside pressure
cabin pressure altitude
equivalent altitude inside of cabin
reduces physical strain on the pilot and pax bodies
cabin differential pressure
difference in pressure between the cabin and the outside air
sonic venturi
limits the amount of air taken from turbo by accelerating air to sonic speed creating a shock wave which acts as a barrier
air is very hot and must be run through a heat exchanger to cool it
after cooling air is sent to cabin via heating and ventilation outlets
regulation
outflow valve - allows air to exit
safety/dump valve - if outflow valves dump will release excess pressure
vacuum relief valve - allows ambient air into cabin
instrumentation
cabin/differential pressure indicator - like altimeter but has two references outside and cabin pressure
cabin rate of climb indicator - indicates rate of change in cabin pressure
altitude at 8,000ft
pressure 10.9 psi
altitude 28,000ft
pressure 4.8 psi
define hypoxia
:lack of sufficient oxygen in the body cells or tissues caused by an inadequate
supply of oxygen, inadequate transportation of oxygen, or inability of the body tissues to use
i. at high altitudes, pressure of oxygen on lungs is reduced, thus, the ability for the body to absorb oxygen is reduced
time of useful consciousness
the amount of time in which a person is able to effectively or adequately perform flight duties with an insufficient
altitude / standard ascent rate / after rapid decompression
18,000 20-30 minutes / 10-15 minutes
22,000 10 minutes / 5 minutes
35,000. 30-60 seconds / 15-30 seconds
50,000. 9-12 seconds / 5 seconds
prolonged use of oxygen
can produce toxic symptoms such as bronchial cough, fever, vomiting, lowered energy
i. significant periods of time are required before this occurs (usually 1-2 days)
decompression sickness
nitrogen in the body changing from liquid form to gaseous
state due to a dramatic reduction in surrounding atmospheric pressure
i. AIM 8-1-2 recommends for flights below 8000 ft (cabin pressure), minimum 12 hours for non-decompression dives, and 2 hours for decompression dives. for flights above 8000 ft, 24 hours minimum.
91.211a - general
i. minimum crew must use oxygen between 12,500 and 14,000 (inclusive) for any period over 30 minutes
ii. minimum crew must use oxygen above 14,000 at all times
iii. all passengers must be provided with oxygen above 15,000
91.211b - pressurized cabin
i. above FL250, minimum of 10-minutes of supplemental oxygen available for each passenger
ii. above FL350, at least one pilot must be wearing and using an oxygen mask; unless at or below FL410, if there are two pilots at the controls, and both have quick donning type mask that can be put on and working within 5 seconds
iii.even with quick donning masks, if one pilot leaves, other must wear and use oxygen until other pilot returns
jet stream
(1) travels east at approximately 50-200 kts
(2) caused by large temperature differences aloft
(3) has a meandering path that is constantly changing
(4) closer to the equator in the winter, farther in the summer
i. general circulation patterns move south in the winter due to less heating activity
clear air turbulence (CAT)
(1) :phenomenon of turbulence associated with high altitude winds, and not associated with
clouds
(2) can be caused by wind shear, mountain waves, low pressures aloft, etc
(3) difficult to forecast since there are no visual signs of it.
supplemental oxygen overview
(1) whether portable or installed, oxygen is stored in high pressure tanks (usually around
1800-2200 PSI)
(2) 22 cu ft container will supply 4 people at 18,000 ft for up to 1.5 hours
(3) aviation oxygen should be the only oxygen to be used (100% oxygen)
i. industrial oxygen is not made for breathing, and has impurities in it.
ii. medical oxygen may contain to much moisture which could freeze at low temperatures
(4) oxygen systems require periodic refill, inspection, and servicing i. AF/D tell what airports have oxygen available
(5) oxygen duration charts allow calculations of time available based on passengers and system PSI
supplemental oxygen continuous-flow
most common type of system for piston aircraft as well as for passengers in turboprop and jets.
(1) overview
i.simplicity keeps maintenance costs down, reduces malfunction possibility
ii. not adequate above 25,000 ft. (although certified up to 41,000
iii. designs may include constant-flow, adjustable-flow, altitude-compensated flow iv. available as built-in system, or portable system
(2) mask styles
i. oronasal rebreather - covers both nose and mouth, and includes a bag to allow reuse of exhaled oxygen
ii. cannula breathing device - oxygen is supplied to the nose only, allowing use of normal communication methods (not certified as high as oronasal rebreathers)
supplemental oxygen diluter-demand/pressure-demand
supply oxygen only when the user inhales through the mask
(1) depending on altitude the supplied mixture of oxygen to cabin-air are automatically adjusted
(2) demand-type masks have a tight seal to avoid dilution by cabin air, and are safe up to 40,000 ft
oxygen generators
(1) available on airliners, oxygen generators use a chemical reaction to produce oxygen for
a set amount of time.
(2) each passenger has an individual “supply” from a generator
cabin pressurization
the compression of air in the aircraft cabin in order to maintain a cabin altitude lower than the actual flight altitude
most light aircraft compress air to the cabin via the turbocharger or an engine-driven pump
pressurization components
i. an outflow valve keeps pressure constant by releasing excess pressure into the atmosphere
ii.a cabin altitude can be manually selected via a cabin altitude controller, and if needed regulated via a backup control to a safety dump valve
iii. vacuum relief valve prevents cabin pressure from becoming lower than ambient pressure in the case of a rapid descent
iv. a heat exchanger conditions the air before entry into the cabin
maximum pressure differential
:maximum allowable difference between atmospheric pressure and cabin pressure
i.different for each aircraft (see POH)
emergency / decompression
the inability of the aircraftʼs pressurization system to maintain its designed pressure schedule
decompression overview
i.can be caused by a malfunction in the system, or by structural damage to the aircraft ii.may result in cabin fog due rapid cooling of relatively moist air
iii.decompression of small cabins is more critical than large cabins given same hole or conditions
(i) primarily due to differences in cabin volume
3 types of decompression
i. slow decompression - may be difficult to detect. many systems include audible and visual warnings of high cabin altitudes
ii. explosive decompression - an extremely dangerous condition in which he aircraft decompresses faster than the lungs can decompress.
(i) typically occurs in less than 0.5 seconds (ii) lung damage can occur
(iii) flying debris may cause further injury
iii. rapid decompression - decompression that occurs quickly, but is slower than the rate at which the lungs can decompress.
decompression recovery
i. use supplemental oxygen as quickly as possible ii. descend as quickly as possible to a safe altitude
(i) a balance between reaching a safe altitude, and taking care of the engine must be made (most significantly in piston engines)
High Altitude Operations - rev. 2/25/09
iii. see emergency descent below for procedure
fuel vaporization
(1) at high altitudes engine driven fuel pumps may be subject to fuel vaporization
i. boost pumps are typically installed to address this situation
severe turbulence
(1) as with any altitude, if severe turbulence is encountered, maintain appropriate airspeed, and attempt to keep wings level, and heading approximately correct
(2) accept changes in altitude and airspeed as long as pitch is relatively constant
Preflight considerations
(1) when using an oxygen system, ensure properly operation by testing the system before
takeoff
(2) when using a pressurized system, refer to the POH to see what preflight actions are required before operation
Emergency Descents
(1) in an emergency descent, the main objective is to lose altitude as quickly (and safely as
possible)
i. may be due to an inflight fire, cabin depressurization, etc.
(2) this objective must be balanced with the need to preserve the engine.
i. especially in Pistons, shock cooling can have significant detrimental effects
(3) Procedure
i. if necessary, don oxygen mask as soon as possible
ii. slow the aircraft to proper speeds to extend gear and flaps
iii. set propeller to high rpm (to help act as an aerodynamic brake)
iv. reduce power as much as practicable
v. if time permits, contact controller and notify of emergency descent for traffic avoidance purposes
vi. initiate a 30°- 45° turn to allow traffic clearing, reduce vertical component of lift, and maintain positive “G” loading on the aircraft
vii. through descent, ensure:
(i) airspeed does not exceed appropriate limitations (Vfe, Vle, Vne) (ii) engine temperature does not cool to rapidly
a. if necessary add power to keep temperature up
Simulated de-pressurization
(1) possible symptoms of a slow leak de-pressurization
(2) upon simulated depressurization
i. fly the airplane!
ii. don oxygen masks asap
iii. refer to emergency descent procedures
signs of hypoxia
confusion, restlessness, difficulty breathing, rapid heart rate, bluish skin, headache, anxiety
