18 Environmental, Oxygen & Ice Protection Practice Questions & Answers
Every Environmental, Oxygen & Ice Protection practice question from the FAA A&P Airframe (AMA) Practice Test, with the correct answer and a short explanation.
Start practice test →1. Cabin pressure in a pressurized aircraft is controlled by regulating the
- A.rate of air flowing into the cabin from the air conditioning packs
- B.speed of the engine driven compressor that supplies the cabin air
- C.rate of air flowing out of the cabin through the outflow valve✓ Answer
- D.position of the negative pressure relief valve in the aft bulkhead
Pressurizing air is supplied to the cabin at a nearly constant rate, so the pressure level is set by how fast that air is allowed to escape. The outflow valve modulates the escaping flow, and therefore it is the component that establishes cabin altitude and cabin rate of change.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
2. A cabin negative pressure relief valve operates when
- A.cabin pressure exceeds ambient pressure, and the valve opens outward
- B.cabin rate of climb exceeds its set limit, and the valve opens inward
- C.ambient pressure exceeds cabin pressure, and the valve opens inward✓ Answer
- D.cabin altitude exceeds the limiter setting, and the valve opens outward
The negative pressure relief valve is spring loaded to open inward so that ambient air can enter whenever outside pressure becomes higher than cabin pressure, such as during a rapid descent. Without it the fuselage skin could be loaded inward and doors could become difficult to open.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
3. In an air cycle air conditioning system, freezing inside the water separator is prevented by a valve that
- A.bypasses warm bleed air into the duct just upstream of the separator✓ Answer
- B.sprays a metered antifreeze mist into the duct ahead of the separator
- C.increases ram airflow through the primary heat exchanger during descent
- D.bypasses cold turbine discharge air around the secondary heat exchanger
Air leaving the expansion turbine is cold enough to freeze the moisture it carries, which would block the separator sock. The refrigeration bypass valve, often called the 35 degree valve, admits warm bleed air into the duct just ahead of the separator to hold the air above freezing while the water is still coalesced and drained overboard.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
4. A continuous stream of bubbles seen in the sight glass of an operating vapor cycle air conditioning system indicates that the system is
- A.correctly charged; no further servicing action is required at this time
- B.saturated with moisture; the receiver dryer element must be replaced
- C.overcharged with refrigerant; part of the charge must be recovered
- D.low on refrigerant; the leak must be found and the system recharged✓ Answer
Liquid refrigerant leaving the condenser should fill the line completely, so the sight glass runs clear when the charge is correct. A steady stream of bubbles means vapor is present in the liquid line because the charge is low, and the correct action is to leak check the system and recharge it with the type and quantity specified by the manufacturer.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
5. An exhaust shroud type cabin heater is inspected for cracks and leaks at the specified interval chiefly because a defect can
- A.allow cabin air to enter the exhaust and start an exhaust fire
- B.allow exhaust back pressure to rise and reduce engine power
- C.allow ram air to escape and reduce the cabin heat available
- D.allow carbon monoxide from the exhaust to enter the cabin air✓ Answer
In this heater, ventilating air is warmed by passing over the exhaust muffler, so any crack in the muffler or shroud lets exhaust gas mix directly with the air ducted to the cabin. Carbon monoxide is colorless and odorless and bonds to hemoglobin far more readily than oxygen, so an undetected leak produces hypoxia-like incapacitation.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
6. Which oxygen system delivers oxygen to the user only during inhalation?
- A.A demand flow system, in which the regulator responds to inhalation✓ Answer
- B.A continuous flow system, in which the regulator meters a steady flow
- C.A chemical oxygen system, in which a candle burns to release oxygen
- D.A liquid oxygen system, in which a converter gasifies the stored supply
Oxygen systems are classified by the type of regulator they use, and a demand regulator opens only when the user draws a breath, conserving oxygen because nothing flows during exhalation or when the mask is off. A continuous flow regulator, by contrast, keeps flowing once the valve is opened whether or not the mask is being used.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
7. Once a sodium chlorate chemical oxygen generator has been ignited, it
- A.can be shut down by closing the manual valve on the generator housing
- B.produces oxygen only while the passenger keeps pulling on the lanyard
- C.continues to produce oxygen until its chemical core is fully consumed✓ Answer
- D.stops producing oxygen as soon as normal cabin pressure is restored
The generator works by burning a sodium chlorate core, and that exothermic reaction cannot be extinguished or throttled once the firing pin or hot wire starts it. It runs for its rated duration, typically on the order of ten to twenty minutes, and the housing becomes very hot, which is why the units are shipped with the ignition device deactivated.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
8. Grease, oil, and other petroleum products must be kept off oxygen system fittings and components because they
- A.can break down the diaphragms inside the pressure reducing valve
- B.can absorb moisture and cause internal corrosion of the cylinder
- C.can ignite violently when they come in contact with oxygen✓ Answer
- D.can clog the calibrated orifices in the continuous flow outlets
Hydrocarbons in contact with oxygen, particularly at the pressures found in an oxygen system, can ignite spontaneously and burn explosively. For that reason tools, hands, clothing, fittings, and servicing equipment must all be free of oil and grease before any oxygen system work is performed.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 16Report a problem with this question
9. Clear ice, as compared with rime ice, forms when
- A.wet snow strikes a warm leading edge and refreezes as a rough crust
- B.large supercooled droplets flow back and freeze as a smooth dense sheet✓ Answer
- C.water vapor sublimates directly onto a cold surface as frost crystals
- D.small supercooled droplets freeze on impact and trap air in the deposit
Large supercooled droplets, typical of rain and cumuliform clouds, do not freeze completely on impact; the remaining liquid runs back along the surface and freezes as a smooth, hard, heavy sheet that adheres tenaciously. Rime ice comes from small droplets that freeze immediately, trapping air and producing a white, brittle deposit that is easier to shed.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
10. In a thermal pneumatic wing anti-ice system, hot bleed air is distributed along the leading edge by
- A.inflatable air cells bonded outside the leading edge
- B.piccolo tubes running spanwise inside the leading edge✓ Answer
- C.electric heating elements laminated in the leading edge
- D.porous laser drilled panels set into the leading edge
Bleed air is fed into perforated spanwise ducts, called piccolo tubes, which spray the hot air against the inside of the leading edge skin so the surface stays above freezing and ice never forms. That preventive action is what distinguishes an anti-ice system from a deice system, which is operated after ice has already accumulated.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
11. In a pneumatic deicer boot system, vacuum is applied to the boots continuously whenever they are not inflating in order to
- A.keep residual ice from bonding to the leading edge skin
- B.raise the boots so the slipstream can blow the ice away
- C.hold the boots flat so they do not disturb the airflow✓ Answer
- D.purge trapped moisture from the air cells before inflation
Continuous suction holds the pliable boot tight against the leading edge contour so the airfoil shape is not spoiled in normal flight, and it also guarantees that the change of shape when the cells inflate is large enough to crack the ice loose. A boot left slack would both degrade the airfoil and shed ice poorly.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
12. During an operational check of a pneumatic deicer boot system, the cycle timing must confirm that
- A.ice is allowed to build to a set thickness before the first inflation
- B.each boot stays inflated until the following boot has inflated
- C.each boot deflates completely before the next boot inflates✓ Answer
- D.the left and right boots inflate one after the other, never together
Inflation must be rapid and deflation must be complete before the next boot inflates, because a partially inflated boot leaves the airfoil distorted and prevents the next cycle from flexing the surface enough to break the ice free. Timing is verified over several complete cycles against the sequence given in the maintenance manual, with an observer outside the aircraft.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
13. Weather cracking in the rubber surface of a pneumatic deicer boot is treated with conductive cement because the cement
- A.seals the crack and insulates the boot from the metal leading edge
- B.seals the crack and drains static charge that would otherwise puncture it✓ Answer
- C.seals the crack and forms a wear layer that resists slipstream erosion
- D.seals the crack and restores the bond between the boot and the wing
The cement is made conductive so that static electricity collected on the rubber can bleed away to the metal structure instead of building up until it arcs through the boot and burns a pinhole in it. Sealing the crack and providing that static path together restore the boot to a serviceable condition.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
14. The temperature of an electrically heated windshield is regulated by a control unit that takes its signal from
- A.thermistors embedded in the windshield laminations✓ Answer
- B.a thermocouple clamped to the windshield bus bar
- C.an ice detector mounted on the forward fuselage
- D.a pressure switch in the windshield vinyl interlayer
Thermistors laminated into the windshield change resistance with temperature, and the window heat control unit uses that signal to switch the transformer supply on and off so the glass is held at its normal operating temperature. A separate thermal overheat switch backs up the controller, and pilot and copilot windows use independent circuits so one failure does not obscure both.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
15. Chemical rain repellent must not be applied to a dry windshield because the undiluted repellent will
- A.harden into a coating that must be removed with an abrasive polish
- B.insulate the heating film and cause the windshield to overheat
- C.attack the vinyl interlayer and delaminate the windshield plies
- D.leave a heavy film that distorts and restricts forward visibility✓ Answer
The repellent is designed to be diluted and spread by impinging rain so that water beads up and is carried away by the slipstream; with no rain to dilute it, it stays as a thick smeared film that badly degrades vision. If it is sprayed inadvertently, the wipers and the rain removal system should not be run because they only increase the smearing, and the residue is rinsed off with fresh water at the first opportunity.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
16. Waste water from galley sinks and lavatory washbasins is carried overboard through drain masts that are
- A.electrically heated to keep the mast and line free of ice✓ Answer
- B.pressurized with bleed air to force the water overboard
- C.routed into the waste holding tank through a check valve
- D.insulated by a shroud fed with warm conditioned cabin air
Gray water is dumped overboard rather than stored, so the mast projects into the airstream where the small flow would freeze and block the line. Electric heaters in the mast and in the drain line, controlled by thermostats, keep the passage open and prevent the ice accumulation that would otherwise back the water up or shed as ice.
Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 15Report a problem with this question
17. In a vacuum waste system on a transport aircraft, the vacuum that moves waste to the holding tank is produced by
- A.a pump driven by the potable water pressurization compressor
- B.cabin differential pressure at altitude and a blower at low altitude✓ Answer
- C.an engine bleed air ejector at all altitudes and also on the ground
- D.a blower at altitude and cabin differential pressure near the ground
Once the aircraft is high enough that cabin-to-ambient differential pressure is large, that differential alone is enough to draw the waste through the lines into the tank, which also acts as the vacuum accumulator. Below roughly that altitude and on the ground the differential is too small, so a vacuum blower is run to create the suction instead.
Source: FAA-S-ACS-1 Aviation Mechanic Airman Certification Standards, Airframe Subject O (Water and Waste Systems)Report a problem with this question
18. When servicing a lavatory waste tank, the drain hose is connected and secured to the service panel before the drain valve is opened in order to
- A.allow the vacuum blower to be tested before the tank is drained
- B.keep the precharge disinfectant from being diluted by rinse water
- C.keep waste from spilling onto the ramp and onto servicing personnel✓ Answer
- D.avoid drawing outside air into the tank and reducing its vacuum
Lavatory waste is a biohazard, so the closed path from the tank to the service cart must be established and secured before any valve is opened, and the technician wears gloves and eye protection. After draining, the tank is rinsed and then given the quantity of precharge or disinfectant specified by the maintenance manual, without overfilling.
Source: FAA-S-ACS-1 Aviation Mechanic Airman Certification Standards, Airframe Subject O (Water and Waste Systems)Report a problem with this question
Practice questions based on the Aviation Mechanic Airman Certification Standards (FAA-S-ACS-1), 14 CFR parts 43, 65, and 91, and the FAA Aviation Maintenance Technician Handbook—Airframe (FAA-H-8083-31). This site is not affiliated with or endorsed by the Federal Aviation Administration. This bank covers the AIRFRAME written test only; the General and Powerplant written tests and the oral and practical tests are separate. Torque values, cable tensions, inflation pressures, servicing quantities, wear limits, and repair criteria always come from the manufacturer's current maintenance data, the structural repair manual, and the applicable airworthiness directives — never from a practice test. Confirm current eligibility and testing requirements with the FAA before you test. About the A&P mechanic certificate →