What is the purpose of AC-120-17A and AC-121-22A ?

Answer 1

120-17A is the document that provides guidelines to an airline that wishes to use it's own maintenance program (instead of the manufacturer's) based on reliability.

Essentially, the airline tracks the manufacturers maintenance program, and on-wing failures for a period of time, then implements it's own program based on it's own reliability history.

For example, if Part A is required to be removed every 2,000 flight hours for overhaul, the airline might look at it each time and find that there is no significant wear and tear, then escalate that inspection interval another 1,000 flight hours with FAA approval. It would then be tracked to dtermine if the interval is too ambitious, or another escalation might be applied if there are no on-wing failures and the 3,000 hour interval is still not showing significant signs of wear. It gives the airlines that ability to design a maintenance program around their actual useage of the aircraft. If you fly fewer hours than some, then you might go to calendar days instead of flight hours.

121-22A is the document that gives manufacturers (i.e. Boeing and Airbus) the ability to write the maintenance program for a new-type aircraft based on the last type.

For instance, when the 747-400 was produced, they used the 747-100/200/300 data to produce the 400's maintenance program. This is also done in conjunction with operators of the 747 series and buyers of the 400. Each airline adds in it's experience, and collectively they write an inspection program for the new aircraft.

For an entirely new-type aircraft, like the 777 was, they all got together and started from scratch. However, for parts and processes the 777 had in common with it's little brothers, they can apply that knowledge, too.

Answer 2

They are both advisory circulars from the FAA.
AC 120-17A Maintenance Control by Reliability Methods
AC 121-22A Maintenance Review Board (MRB) Procedures

Answer 3

Pertaining to the FAA, AC stands for advisory circulars under regulations and guidelines. Looking up the numbers only 120-17A comes up with info for maintenance personnel. Where did you get these numbers from?

Answer 4

To answer your question about AC 120-17A Maintenance Control by Reliability Methods and AC 121-22A Maintenance Review Board Procedures you need to understand they are both explain part of the Continuing Analysis and Surveillance System (CASS) program all air carriers function under. This is a very difficult subject to try and explain, so I will provide a short part of it.

Each AC has an introduction statement that explains what the AC is for. Most AC’s will explain how to meet the Federal Regulation it relates to. In the case of AC 120-17 it is about air carriers under Title 49 Part 121 and 127 (these are the big guys like United, American, Delta, United Express, Sky-West and so on)

AC 120-17 that states:
1. PURPOSE. This publication provides information on the application of reliability control methods as an integral part of an approved aircraft maintenance program for operators subject to the provisions of Federal Aviation Regulations, Parts 121 or 127.

a. Its primary objective is to provide guidance for development of programs using reliability techniques. It expresses Federal Aviation Administration practice with regard to control programs utilizing these techniques.

AC 121-22A states:
PURPOSE. This advisory circular (AC) provides guidelines that may be used by industry during its development and revision of the initial minimum scheduled maintenance/inspection requirements for derivative or newly type-certificated transport category aircraft and powerplants for submittal to the Federal Aviation Administration (FAA) for approval. These initial minimum scheduled maintenance/inspection requirements are referred to in this AC as the Maintenance Review Board Report (MRBR). The requirements, after approval by the FAA, become a base or framework around which each air carrier develops its own individual maintenance program.

Not to confuse you both of these AC’s explain to the air carriers how to develop a Continuing Analysis and Surveillance System (CASS) program to perform aircraft maintenance.

Customers operating under 121, 129, 135 (ten or more) must have a CASS Program

The Air Carrier must demonstrate that they are:
· Following their inspection and maintenance manuals and procedures
· Producing consistently airworthy aircraft
· This includes aircraft that are maintained by third parties

Programs track:
· Maintenance related delays and cancellations
· Failure rates of parts and components approved for return to service
· Discrepancy rates of aircraft after heavy maintenance
· Related trend analysis

CASS is intended to give an operator [and the FAA] a realistic picture of the frequency and nature of deficiencies occurring in the operator’s maintenance programs, and the opportunity to correct them. Some other AC’s explain different parts of the CASS as follows:

AC References:
(1) AC 00-46, Aviation Safety Reporting Program, as revised.
(2) AC 20-41, Substitute Technical Standard Order (TSO) Aircraft Equipment, as revised.
(3) AC 20-62, Eligibility, Quality, and Identification of Aeronautical Replacement Parts, as revised.
(4) AC 20-77, Use of Manufacturers' Maintenance Manuals.
(5) AC 20-114, Manufacturers' Service Documents.
(6) AC 120-16, Continuous Airworthiness Maintenance Programs, as revised.
(7) AC 120-17, Maintenance Control by Reliability Methods, as revised.
(8) AC 121-1, Standard Operations Specifications Aircraft Maintenance Handbook, as revised.
(9) AC 121-22, Maintenance Review Board (MRB), as revised.
(10) AC 120-12 Private Carriage Versus Common Carriage of Persons or Property.
(11) AC 120-59 Air Carrier Internal Evaluation Programs.
(12) AC 120-79 Developing and Implementing a Continuing Analysis and Surveillance System

The FAA implemented the requirement for a CASS in 1964 in response to safety concerns and discoveries of weaknesses in the airworthiness programs of some operators, as revealed during accident investigations and FAA surveillance of operator maintenance activities. The FAA issued the requirement in conjunction with other regulations designed to strengthen requirements for air carriers' inspection and maintenance organizations and activities.

Advisory circular (AC) 120-79, provides information and guidance material that may be used by air carrier certificate holders, operating under Federal Aviation Regulations (FAR) Parts 121 and 135, to design or develop an Internal Evaluation Program. The procedures and practices outlined in this AC can be applied to maintenance, flight operations, and security aspects of an air carrier's organization. Internal evaluation guidance for certificate holders other than those operating under FAR Parts 121 and 135 may be issued separately in the future.

Hope I have shed some light on this for you.