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Quizzes > Science

2A551B URE Quiz: Test Your CDCs Volume 2 Knowledge

Quick CDCs 2A551 practice test with instant results and answer review.

Editorial: Review CompletedCreated By: Joseless KingUpdated Aug 26, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art style illustration showing aerospace maintenance stands, jacks, and procedural icons on golden yellow backdrop.

This quiz helps you check your 2A551 CDC Volume 2 URE knowledge on stands, jacks, and procedures before test day. Get instant results, see answers with brief notes, and track weak areas in minutes. For more coverage, try the 2a653 cdc vol 1 quiz and brush up on supply basics with the afman 23-110 quiz.

What is the primary purpose of a droop stop on an aircraft stand?
To prevent overextension of landing gear struts
To limit wing droop when weight is removed
To measure hydraulic pressure in the stand
To secure the stand to the jack pad
A droop stop prevents excessive wing droop after landing gear weight is removed, protecting wing structure. It engages when strut extension exceeds design limits. Proper use ensures wing integrity during maintenance.
Which type of jack is commonly used for initial lift of nose gear?
Bottle jack
Scissor jack
Pneumatic jack
Electric trolley jack
Bottle jacks provide high capacity in a compact form and are often used for initial lift of nose gear. Their vertical design suits landing gear pick points. Technicians select them for simplicity and load rating.
Before jacking, what is the minimum required number of safety stands to be placed under an aircraft wing?
One per wing
Two per wing
One per supported point
Four per wing
Safety stands must be placed at each designated support point to prevent unexpected drop. This ensures structural support if the jack fails. Stand placement follows the aircraft maintenance manual.
What component on a hydraulic jack indicates fluid level?
Sight glass
Bleeder valve
Pressure gauge
Relief valve
A sight glass on a hydraulic jack lets technicians observe the fluid level without disassembly. Correct fluid level ensures proper pump function and prevents damage. It’s essential for jack maintenance.
When inspecting a stand, what should you check for wear?
Paint color
Pad condition
Wheel size
Handle length
Stand pads must be free of cracks, tears, or excessive wear to ensure safe support. Worn pads can slip or cause damage to aircraft surfaces. Regular inspection protects both stand and airframe.
What is the static load of an aircraft?
Load while taxiing
Weight when parked on ground
Weight in flight
Engine thrust force
Static load refers to the aircraft’s weight at rest on the ground with no external forces. It’s critical for selecting stand and jack capacities. Maintenance manuals specify static load values.
Why is it important to use jack pads when jacking an aircraft?
To reduce noise
To protect the aircraft structure
To increase lift speed
To stabilize hydraulic pressure
Jack pads distribute jack load over a larger area of the aircraft structure to prevent damage. They are designed to fit designated lift points. Using pads safeguards skin and assemblies.
What should you do if a jack begins to lose pressure during an operation?
Continue and monitor
Lower aircraft and inspect jack
Add more hydraulic fluid while under load
Apply lubricant to the piston
If pressure loss occurs, lower the aircraft safely, then inspect the jack for leaks or damage. Operating with pressure loss is unsafe. Corrective action prevents accidents.
Which safety device prevents a stand from collapsing if the latch fails?
Safety pin
Pressure gauge
Hydraulic lock
Overload valve
Safety pins lock stand legs into position in case the latch or ratchet fails. They are a critical secondary device. Always install pins before removing primary support.
How often must stands be inspected for corrosion before use?
Daily
Weekly
Monthly
Annually
Daily inspections for corrosion ensure stands maintain structural integrity. Corrosion can weaken legs or locks leading to failure. A quick check prevents accidents during jacking.
What is the correct action if you discover a bent stand leg?
Straighten it with a hammer
Use it only for light loads
Tag out and remove from service
Weld it back into shape
Bent stand legs compromise stability and must be removed from service. Tagging out prevents accidental use. Only certified equipment should support aircraft.
What identifies the load capacity of a jack?
Paint color
Stamped rating plate
Handle length
Pad diameter
Jack capacity is stamped on a metal rating plate attached to the unit. Never exceed the rated capacity. This ensures safe lifting operations.
Which fluid property is most critical in hydraulic jack performance?
Viscosity
Color
Odor
pH level
Viscosity affects how fluid flows under pressure and at various temperatures. Proper viscosity ensures smooth, efficient jack operation. Use manufacturer-recommended hydraulic fluid.
Why must you chock wheels before jacking?
To prevent brake wear
To secure aircraft against movement
To align the jack
To reduce noise
Wheel chocks prevent the aircraft from rolling when jacked. They are a fundamental safety step. Always place chocks even on level surfaces.
What indicates a hydraulic jack seal is leaking?
Piston movement slows under load
Handle becomes loose
Pad shifts sideways
Stand legs wobble
A leaking seal causes internal fluid bypass, reducing lifting speed and load-holding. You may see fluid around seal area. Replace seals before next use.
How do you calculate the required jack capacity for a given wing section?
Divide aircraft gross weight by four
Use weight and balance chart to find wing load
Estimate 30% of total weight
Multiply static load by gear ratio
The weight and balance chart provides the actual load on each wing support point. You select jack capacity equal or above that load. This ensures safe lifting.
What thread pitch on a mechanical jack influences lift per handle stroke?
Coarse thread pitch
Fine thread pitch
Acme thread pitch
Metric thread pitch
Coarse threads move more per rotation, resulting in faster lift per stroke. Fine threads require more rotations for the same lift but offer finer control. Correct selection balances speed and precision.
During an outboard wing jack, which device controls wing cantilever bending?
Shear block
Load cell
Reaction rod
Torque wrench
Reaction rods attach from wing to fuselage to resist bending moments during outboard wing jacking. They protect structural integrity. Proper attachment per manual prevents damage.
What is the effect of temperature on hydraulic jack performance?
Higher viscosity at low temperatures slows operation
Temperature has no effect
Fluid volume decreases in heat
Seals expand in cold improving performance
Hydraulic fluid viscosity increases at low temperatures, causing sluggish movement. At high temperatures, viscosity drops, risking leaks. Always use recommended fluid and precondition as needed.
When leveling an aircraft on jacks, which instrument is used to ensure correct attitude?
Digital inclinometer
Tire pressure gauge
Altimeter
Compass
A digital inclinometer measures precise pitch and roll angles. It helps achieve the correct aircraft attitude when jacked. This is essential for maintenance requiring level reference.
How should jacks be positioned relative to the designated jacking point?
Offset on one side
Centered directly under point
Angled toward fuselage
Touching adjacent structure
Jacks must be centered under the approved jacking pad to evenly distribute load. Misalignment can damage structure or cause jack failure. Always follow the maintenance manual diagram.
What pressure relief device prevents overloading a hydraulic jack?
Check valve
Relief valve
Pressure gauge
Flow restrictor
A relief valve opens when system pressure exceeds a set limit, protecting the jack and structure. It prevents catastrophic failure from overload. Regular testing ensures proper function.
Which calculation is required to centre an aircraft accurately on multiple jacks?
Total load divided by number of jacks
Moments about longitudinal axis
Wing chord length
Gear torque values
Balancing moments about the longitudinal and lateral axes ensures correct centering. You calculate each jack’s load contribution to maintain attitude. This prevents structural stress.
What maintenance action is required if jack handles are bent?
Use only on lighter loads
Replace handle per tm
Straighten and paint
File down bent area
Bent handles compromise leverage and safety. Technical order requires replacement with correctly specified parts. This ensures proper operation.
Which reference details the correct stand placement for engine change?
Aircraft flight manual
Structural repair manual
Technical order (TO)
Maintenance safety guide
Technical Orders (TOs) provide exact procedures and diagrams for engine changes. They specify stand positions, load limits, and sequence. Always follow the TO.
Why is synchronization important when using multiple jacks on a large aircraft?
Improves hydraulic fluid life
Prevents twisting and structural stress
Reduces noise
Increases jacking speed
Unsynchronized jacks can lift unevenly, causing torsional stress and potential damage. Proper synchronization maintains structural alignment. Systems or manual checks ensure uniform lift.
What is the correct sequence when lowering an aircraft on jacks?
Remove stands, lower jacks, remove pads
Lower jacks slowly, remove stands and pads
Remove pads, lower jacks, then stands
Lower jacks quickly, then stands
Lowering jacks slowly prevents sudden settling. Once aircraft touches stands or ground, remove safety stands and pads. This order ensures controlled descent.
How do you verify jack tare weight before use in multi-jack leveling?
Consult jack manufacturer
Zero the jack scale under no load
Use static load value
Estimate weight of oil
Zeroing the scale under no load sets tare weight for accurate measurement. This ensures corrected lift readings during leveling. Follow the jack manual procedure.
How do you calculate the bending moment on a wing during an inboard jack lift?
Fluid pressure × jack area
Lift force × distance from CG
Aircraft weight ÷ number of jacks
Wing area × air density
The bending moment equals the lift force applied by the jack multiplied by its distance from the center of gravity. This calculation predicts structural load. Correct values ensure safe jacking procedures.
What is the effect of backlog in a hydraulic system on jack performance?
Increases lifting capacity
Causes spongy operation and delayed response
Reduces fluid temperature
Improves seal life
Backlog or trapped air in the system can compress under load, causing slow or spongy jack response. Bleeding the system restores firm operation. Regular maintenance prevents air intrusion.
During high-angle jacking, which factor must be compensated for in load calculations?
Reduced gravity effect on weight vector
Increased hydraulic pressure requirement
Wing deflection
Fluid thermal expansion
High-angle jacking changes the direction of the lift vector, altering the effective load component. You must calculate the vertical component of force. This prevents underestimating jack capacity.
What procedure corrects misalignment of a stand leg after initial setup?
Bend leg to fit
Lower stand and reposition under the load point
Tighten the latch further
Place shim under pad
If a stand leg is misaligned, you lower and reposition to align properly with the load path. Bending or shimming is not authorized. Proper alignment distributes load evenly.
Which inspection step follows pressure testing a jack after overhaul?
Bleed the air and recheck performance
Paint the jack
Add sealant to threads
Tighten all bolts to max torque
After pressure testing, trapped air must be bled to ensure consistent operation. Then performance is rechecked under load. This final step validates the overhaul.
How do you determine if a support stand meets fatigue life requirements?
Check the service diary for inspection dates
Review maintenance technical order for life limits
Compare stand color code
Inspect weld seams only
Technical orders list stand life limits and mandatory inspections. Reviewing these ensures stands remain within fatigue life. Color coding or weld inspection alone is insufficient.
Which calculation is used to adjust jack placement for a shifted center of gravity?
Moment index adjustment
Wing loading factor
Gear ratio compensation
Strut length modification
When CG shifts, you recalculate the moment index to reposition jacks under proper load points. This ensures stable and accurate leveling. Manuals provide formulas for moment adjustments.
In multi-point jacking, what causes differential lift rates between jacks?
Unequal fluid temperatures
Varying stand heights
Discrepancies in tare calibration
Jack pad material differences
If jacks are not tare-calibrated equally, some carry more load, causing uneven lift rates. Ensuring each jack is zeroed and synchronized prevents this.
Which advanced tool helps monitor load distribution in real time during jacking?
Digital torque wrench
Load cell with data logger
Ultrasonic thickness gauge
Infrared thermometer
Load cells with data loggers provide continuous load readings on each jack. They help technicians adjust jacks to maintain balance. This advanced monitoring enhances safety.
What modification may be needed for jacking on composite wing surfaces?
Use shims under pads
Install custom composite pad adapters
Increase jack pressure
Apply sealant to contact area
Composite adapters conform to wing curvature and distribute load without damaging the skin. Standard pads can cause cracks on composites. Adapters are specified in the maintenance manual.
Which factor must be considered when storing jacks long-term?
Humidity and corrosion protection
Oil color matching
Handle removal
Wheel alignment
High humidity can corrode internal components. Jacks should be stored in dry, climate-controlled areas and coated lightly with rust inhibitor. Proper storage extends service life.
During recovery from a jack failure, what is the first corrective action?
Increase hydraulic pressure
Apply emergency stands before lowering
Call manufacturer
Drain fluid from jack
Emergency stands provide temporary support to prevent collapse. Once stands are in place, you can safely lower and inspect the jack. This sequence minimizes risk.
For a three-point synchronized jacking operation, which algorithm ensures equal load distribution?
Simple average of loads
Weighted moment-balanced algorithm
Pressure differential method
Torque feedback loop
A weighted moment-balanced algorithm uses moment arms and load cells to continuously adjust jack pressures for equal distribution. This advanced method prevents twisting. It’s specified in advanced maintenance procedures.
How is structural resonance avoided during rapid multi-jack lifting?
By lifting in small, varied increments
By using higher viscosity fluid
By applying temporary braces only
By pausing halfway through lift
Small, varied increments prevent exciting the structure’s natural frequency. This technique avoids resonance that could cause fatigue or damage. Advanced procedures emphasize controlled, incremental jacking.
What method verifies integrity of composite adapter?pad interface under cyclic load?
Visual inspection only
Ultrasonic bond-line testing
Magnetic particle inspection
Dye penetrant
Ultrasonic testing can detect disbonds and internal flaws at the adapter interface. It’s non-destructive and reliable under cyclic jacking loads. This advanced inspection is required for composites.
In an emergency under-wing jacking, which factor takes priority in jack placement?
Minimizing spanwise bending moments
Proximity to fuselage
Maximizing pad area
Ease of access
Under-wing jacking in emergencies focuses on minimizing spanwise bending to protect wing integrity. Positioning jacks close to load-bearing spars reduces bending moments. Expert crews follow specific emergency procedures.
How do you adjust multi-jack synchronization for a long-term load shift during maintenance?
Rebalance using real-time load cell feedback and algorithm update
Increase all jack pressures by 10%
Swap stand positions mid-operation
Use manual override on one jack
Real-time load cell feedback allows dynamic adjustment as weight shifts occur. Updating synchronization algorithms maintains balance throughout long operations. This advanced procedure ensures continuous safety.
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Study Outcomes

  1. Understand Maintenance Stand Types -

    Gain knowledge of different maintenance stands used in 2a551B operations, including their configurations and load capacities.

  2. Identify Scissor-Type Stand Features -

    Learn to recognize the key safety features and proper usage of scissor-type stands within aerospace maintenance.

  3. Apply Aircraft Jacking Procedures -

    Practice correct jacking techniques to ensure safe lifting and support of aircraft components during maintenance.

  4. Analyze 2A551 CDCs Equipment Protocols -

    Interpret equipment manuals and troubleshooting steps outlined in 2A551 CDCs Volume 2 to enhance procedural accuracy.

  5. Evaluate Your Aerospace Maintenance Skills -

    Use this free scored quiz to assess your proficiency, identify knowledge gaps, and focus on areas needing improvement.

Cheat Sheet

  1. Load Capacity & Stability -

    Maintenance stands must be leveled so an aircraft's center of gravity (CG) stays within the stand's stability triangle at all times. Calculate load per stand by dividing the aircraft's weight by the number of supports and then adding a 10% safety margin - this quick check builds your confidence before every job. Always cross-check the stand's rated capacity on the frame against Technical Order (T.O.) specifications to prevent overloading.

  2. Scissor-type Stand Inspection -

    Before use, inspect scissor stands for bent linkages, loose pivot pins, and hydraulic fluid leaks per MIL-STD-1762 guidelines. Use the mnemonic "PIVOT": Pins secure, Integrity intact, Viscosity correct, Oil level sufficient, Tight fasteners. These proactive checks keep you sharp and safe on every maintenance task.

  3. Aircraft Jack Positioning & Load Distribution -

    Position jacks only at approved jack points as outlined in the aircraft's T.O., ensuring equal lift to each fuselage station. Divide the aircraft's weight by the number of hydraulic jacks and monitor gauge readings to maintain level lift. A simple check: all pressure gauges should read within ±50 psi of each other throughout the operation to guarantee a level lift and peace of mind.

  4. Pascal's Law & Hydraulic Jack Operation -

    Hydraulic jacks rely on Pascal's Law (P = F/A) to amplify force; a small input force on a pump piston creates a larger output force on the jack cylinder. Always verify pump reservoir fluid is at the correct level and free of contamination. These simple pre-use checks ensure your jack performs reliably under load.

  5. Safety Locking & Grounding Procedures -

    Once the aircraft is elevated, insert safety pins or locks into every stand and jack to prevent collapse in case of hydraulic failure. Apply static grounding straps to avoid electrostatic discharge, following AFMAN 91-203 guidelines. This "Lock, Tag, Ground" habit not only meets standards but also boosts team trust in your safety protocols.

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