Aircraft Maintenance: Tolerance and Allowance

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Questions and Answers

What is typically found in a block or placed in a location that does not interfere with the drawing?

Title block

Bill of material

Revision block

Notes (correct)

What is the purpose of the APPLICATION block in a drawing?

To provide notes on the drawing

To show the model of aircraft the part is used on and the part number of the next assembly (correct)

To list the materials needed to manufacture the part

To record revisions to the drawing

What is usually located in the upper right corner of a drawing?

Revision block (correct)

Title block

Notes block

Bill of material

What information can be found in the title block of a drawing?

The quantity required, part number, description, size, and specification number for the materials needed Signup and view all the answers

What is the purpose of notes in a drawing?

To identify a deviation from the norm, provide additional information, list alternatives, or specify modifications to an original design Signup and view all the answers

What is the primary function of the bill of material in a drawing?

To list the materials needed to manufacture the part Signup and view all the answers

What type of tolerance shows variation from a target dimension in both positive and negative directions?

Bilateral tolerance Signup and view all the answers

What is the minimum clearance or maximum interference between mating parts?

Allowance Signup and view all the answers

What is the term for the condition in which a feature of a finished part contains the maximum amount of material?

Maximum material condition Signup and view all the answers

What is the term for the clearance or interference that gives the tightest possible fit between mating parts?

Allowance Signup and view all the answers

What is the result when a hole is smaller than the shaft or item being placed into the hole?

Interference Signup and view all the answers

What is the calculation for the allowance in the given example?

Tolerance on the shaft + Tolerance on the hole Signup and view all the answers

What is the ideal way to clean lenses, mirrors, and viewing screens?

With extreme care to avoid damage or smearing Signup and view all the answers

How many pages of text can a microfiche card hold?

Between 98 and 133 pages Signup and view all the answers

What is the primary purpose of the microfiche filing number?

To locate the card within the set Signup and view all the answers

How long does it take to learn to use the microfiche system?

Less than 15 minutes Signup and view all the answers

What is the purpose of the introductory page on a microfiche card?

To provide ordering and publisher's information Signup and view all the answers

What is the typical size of a microfiche card?

4 × 6 in. Signup and view all the answers

Which standard was developed by the US military to ensure quality and uniformity?

AN Signup and view all the answers

What is the purpose of cross-referencing AN and MS hardware?

To ensure proper replacement with identical characteristics Signup and view all the answers

What is true about items manufactured to the AN standard?

They are found in all classifications of aircraft Signup and view all the answers

What is the relationship between AN and MS standards?

MS and AN are interchangeable Signup and view all the answers

What is the status of the AN system?

It is being replaced by the MS and NAS systems Signup and view all the answers

What is common to all the standards mentioned?

They are all ISO 9000 compliant Signup and view all the answers

What is the primary purpose of MIL-STD standards?

To ensure a certain level of performance and maintainability of military equipment Signup and view all the answers

What is the main focus of NAS system?

Providing design and process standards for the civilian aerospace industry Signup and view all the answers

What is the role of NSO in standards development?

Developing military operational standards for NATO military alliance Signup and view all the answers

What type of standards does MIL-STD represent?

Military standards developed by the United States Military Signup and view all the answers

What is the relationship between NSO and civilian SDOs?

NSO influences civilian SDOs Signup and view all the answers

What type of equipment does MIL-STD ensure the performance and maintainability of?

Military equipment, including aviation parts and equipment Signup and view all the answers

Study Notes

Title Block and Bill of Material

The title block includes essential information like part number and title.
Directly above the title, a bill of material lists every material required, including quantities, sizes, and specification numbers.

Application Block

The APPLICATION block specifies the aircraft model and part number for use.
Shows the quantity of parts needed for both the next assembly and the final assembly.

Notes on Drawings

Notes provide additional insights, deviations, alternatives, or modifications related to the drawing.
Typically placed in a dedicated block to avoid interference with the main drawing.

Revision Block

Located in the upper right corner of a drawing to record all revisions.
Bilateral tolerance indicates variation from target dimensions in both positive and negative directions.

Allowance in Mechanical Fitting

Allowance refers to minimum clearance (positive) or maximum interference (negative) between mating parts.
Clearance indicates no contact, while interference means components won't fit properly.

Maximum and Least Material Condition

Maximum Material Condition (MMC) is when a part has the most material, like the largest shaft or smallest hole.
Least Material Condition (LMC) represents the least amount of material, as in the smallest shaft or largest hole.

Example of Allowance

For a basic size of 1.500 inches and tolerances of 0.002 inches (shaft) and 0.001 inches (hole), the allowance for tightest fit is 0.004 inches.

Microfiche System

Microfiche cards (4 × 6 inches) hold 98 to 133 pages of text, magnified by microfiche readers for viewing.
Familiarity with this system can be achieved in less than 15 minutes.

Features of Microfiche Cards

Each card displays a title clearly in a yellow strip.
Index numbers facilitate easy locating within the set.
Introductory pages include ordering and publisher information.

Standard Specifications Overview

Major standards: AN (Air Force/Navy), NAS (National Aerospace Standard), MS (Military Standard), MIL (Military Specification), NSO (NATO Standardization Office).
Compliance with ISO 9000 is common across these standards, ensuring quality and consistency.

AN Specifications

AN system ensures quality and uniformity in aircraft hardware developed by the US military.
Although deemed obsolescent, AN parts are still used and fitted in new aircraft.

MS Specifications

Based on military development, MS specifications are widespread in aviation.
Cross-referencing allows substitution with caution to maintain proper characteristics.

NAS Specifications

NAS standards support both military and civilian aerospace sectors, detailing fastener requirements and specifications.
Covers aspects like head markings, plating, and locking requirements.

MIL Specifications

MIL-STD items are designed to meet US Military Standards, ensuring certain performance and maintainability in military hardware.

NSO Specifications

The NATO's NSO develops military operational standards to enhance interoperability among alliance forces.
Collaborates with civilian standards-developing organizations for effective engineering practices.

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Description

Test your knowledge of bilateral tolerance and allowance in aircraft maintenance. Learn about the minimum clearance and maximum interference between mating parts and how it affects the fit.