Volume 4 AIRCRAFT EQUIPMENT AND OPERATIONAL AUTHORIZATIONS
Chapter 3 AIRPLANE PERFORMANCE AND AIRPORT DATA
Section 3 Safety Assurance System: Approval of Performance Data Sections of CFMs
4-546 GENERAL. This section contains information and guidance to principal
operations inspectors (POI) for reviewing and approving the presentation of
performance data in Company Flight Manuals (CFM). For guidance on the approval of manuals see
Volume 3, Chapter 32, Section 2. This
section is related to Safety Assurance System (SAS) Element 3.2.1 (OP), Aircraft Performance Operating Limitations.
A. Performance Data Computation Systems. A performance data computation
system is defined as the system the operator uses to produce the data required
to operate an airplane within the performance limitations specified in the Airplane
Flight Manual (AFM) and subpart I of either Title 14 of the Code of Federal Regulations (14 CFR) part
121 or part
applicable. The performance data computation system consists of at least the following components:
1) An airport data acquisition, maintenance, and dissemination
system (a necessary subsystem for all airplanes operated under parts
NOTE: The majority of this data is available from commercial and government
aeronautical charting services. Operators of large transport and commuter category
airplanes, however, require obstacle data for takeoff computations that are
more detailed than those usually supplied by a standard charting service. Operators
may contract for obstacle data from commercial sources or may collect the data
themselves. Specific guidance for the acceptance or approval of airport data
acquisition systems is in
Volume 4, Chapter 3, Section 4.
2) Performance data for each variant aircraft the operator operates
in a format readily usable by the flightcrew. (This data may be obtained from
the AFM directly or purchased in a digital format suitable for computer processing.)
3) Manual computation procedures or a computer algorithm for
converting aircraft performance data from the AFM format to the format used
by the flightcrew. (The system must make all necessary computations for determining
the maximum allowable weight for takeoff and for determining the V speeds to
be used at the selected weight.)
B. Current Industry Practices. There are a wide range of methods
for: collecting airport and obstacle data; preparing airport analyses; and preparing,
publishing, and distributing the performance data sections of CFMs. To implement
each or all of these functions, operators may either establish a department
within the company or contract the work out. Operators may contract for the
collection of airport and obstacle data but produce the airport analysis in‑house.
Other operators may supply airport data to aircraft manufacturers or other contractors
who prepare the airport analysis. Generally, major airlines do more of this
process in-house, while smaller operators contract for these services. Some
service contractors provide services tailored specifically to part
121 supplemental and part
135 on‑demand operators.
C. Approval Criteria. POIs may approve any method of performance
data computation and presentation that meets the following criteria:
1) The system must make all of the computations required in the
AFM and in the pertinent operating rules (see
Volume 4, Chapter 3, Section 2 for
a description of these factors for specific airplanes).
2) Provisions must be made in the system for all makes, models,
and variations of aircraft used by the operator.
3) The system must account for all pertinent variables such as
temperature, weight, thrust, runway condition, and obstacles.
4) The system must be appropriate to the operator's requirements.
Large, highly complex airplanes usually require very different systems from
those required for small, simple airplanes.
5) The system must be reliable in that identical answers must
be generated each time the process is entered with identical parameters.
6) The system must be accurate in that it generates performance
data that agrees with AFM data within the degree of accuracy inherent in the
original AFM data. For example, when the AFM data is accurate to +2 percent,
the operator's system must produce results that do not deviate from the AFM data by more than +2 percent.
7) The system should be relatively simple, easy to use, and not error-prone.
8) When simplifying assumptions are made, those assumptions must
be clearly and completely stated in the operator's CFM or General Operations
Manual (GOM) as operator-imposed limitations (for example, a maximum field elevation
of 4,000 feet and minimum runway length of 5,000 feet). When the assumptions
cannot be met, the actions to be taken by the flightcrew, flight followers,
and dispatchers must be clearly specified. In such cases, operations must be
prohibited or alternate procedures specified.
9) The flightcrew procedures for generating, obtaining, and verifying
data must be thoroughly described in the procedures section of the CFM. In the
case of the same procedure applying to all airplanes, the flightcrew procedures
must be described in a section of the GOM.
4-547 MANUAL COMPUTATION SYSTEM FROM AFM DATA. Operators may choose to
have flightcrew members, dispatchers, or flight followers conduct manual data computations from the AFM
performance section for each takeoff. Equipment is not necessary to establish the manual computation system. This
system is flexible because it can be used for any runway for which the required input parameters can be
obtained. The disadvantage of such a system is that computations can be difficult, complex, time consuming,
and error prone. Flightcrew members, flight followers, and dispatchers must be carefully and thoroughly trained
in such a system. Flightcrews must be supplied with the location of the controlling obstacle for each runway
used. While this system is widely used for small airplanes, it is impractical for the routine operations of
large airplanes because of the complexity of the required computations and the high probability of human error. The
system is, however, available to the operator for backup in the case of computer failure and for special one time requirements.
4-548 TABULATED DATA METHOD. AFM data may be combined with airport and
runway data and published in tabular format. The product of this tabulated data method is usually termed an airport
analysis. Typically, the flightcrew is provided with a table for each runway and flap setting. The flightcrew member
enters the temperature on the table to determine maximum allowable takeoff weight and then enters the actual weight to
determine the V speeds. Additional corrections are required for factors such as wet or contaminated runways and winds.
A. Tabulated Data. Tabulated data is easier to use, less error
prone, and requires less training than is required for AFM data. A properly
designed CFM system retains most of the operating flexibility of the AFM system.
A tabulated data system reduces, but does not eliminate, human error. A disadvantage
of the tabulated data system is that crewmembers must maintain an up-to-date
chart for each runway from which operations are authorized. A means must be
available to transmit current charts to the flightcrew before they are needed.
Provisions must be made for temporarily shortened runways.
B. Generating Performance Data Tables. The operator must be capable
of generating performance data tables which retain the degree of accuracy inherent
in the AFM data. Generally, this must be done manually, by carefully picking
data points from a graph, entering the data into a computer, and carefully verifying
the generated points. The amount of work required to prepare tabulated data
from an AFM often precludes operators from generating their own data packages.
Most often the operator will be required to buy a digital data package from
the manufacturer from which to generate the required tables. POIs may approve
other sources, however, when the operator can adequately establish the accuracy of the data.
C. Performance. The operator's system must be capable of performing
all of the required computations for each takeoff situation, including the selection
of the correct controlling obstacle for each flap setting.
4-549 SIMPLIFIED DATA METHOD. A simplified data system is based on a specified
set of assumptions about the conditions under which the aircraft will be operated. For example, takeoffs
might be limited to runways longer than 5,000 feet and less than 4,000 feet elevation. In this system, the
crew is supplied with a simple chart or set of cards which gives the V speeds at specified weight increments. This
chart is used on all runways. The operator performs an airport analysis for each airport served and demonstrates
that when the aircraft is operated in accordance with the specified set of assumptions, it will perform either equal
to, or better than, the performance required in the applicable regulations on all runways the crew is authorized to use.
A. Advantages. Some of the system's advantages are:
its relative simplicity, the lack of crew error, the ease of crew training,
and the speed with which the crew can determine V speeds.
B. Disadvantages. Some of the system's disadvantages are: it
often imposes severe performance penalties on operators, it is inflexible, and
operations must either be terminated or an alternate system used when the simplifying
assumptions cannot be met (for such conditions as construction, part of runway
closed, ice, rain, or shortened runways).
C. The system is best suited for operators who serve a limited
number of locations regularly and who operate either at large airports, near sea level, or at moderate temperatures.
4-550 REAL TIME METHOD. A real time data system is one in which the required
computations are made immediately before takeoff for every flight. Usually the data is relayed to the flightcrew by
radio or through Aircraft Communications Addressing and Reporting System (ACARS). The advantages of such a system are
that it is extremely flexible, up to date, and efficient. Changes in obstacles due to construction, weight, temperature,
and runway can be handled immediately. Also, the operator can take maximum advantage of the performance capabilities of
the airplane. Some disadvantages of the system are that it is expensive, it requires extensive equipment and highly trained
personnel to operate, and that adequate backup must be available should the main computer go offline. The operator must be
able to collect all of the required data, process it, and transmit it to the crew quickly.
4-551 EVALUATION OF AN OPERATOR'S SYSTEM. Generally, POIs do not have the capability to
verify each data point when approving the performance data section of a CFM. The validity and reliability of the
computation system itself, however, can be evaluated.
A. Provide Analysis. POIs shall require the operator to provide
an analysis, with documentation, of the following:
· Source of the computer program;
· Assumptions on which the computer program is based (for example,
they must determine if the correct factors are used for each type of aircraft; see
Volume 4, Chapter 3, Section 1);
· Source and accuracy of the databases used;
· Operator's capability for handling data; and
· Results of parallel manual calculations made with AFM data to confirm results.
B. Coordinate. The POI should coordinate with the principal maintenance
inspector (PMI) to ensure that the operator's airplanes meet the specifications
of the certification regulations. For example, a small airplane may have been
modified to install more than the original nine seats. To qualify under the additional airworthiness standards of part
A, several modifications that require Supplemental Type Certificates
(STC) may have been required. Unless all of the required modifications have
been completed, the airplane may not qualify for the proposed operation.
C. Responsible. When the operator contracts for data or computation,
the operator is responsible for the validity of the results. A POI may find
that the contractor has been previously evaluated and approved for another operator.
The POI may approve reputable sources for these services that have been previously
evaluated without the documentation discussed in subparagraph 4-551A. POIs who
are concerned about a specific contractor's qualifications should contact the
regional Flight Standards division (RFSD), who may, in turn, coordinate with
the Air Transportation Division (AFS-200). If the contractor's capabilities
and qualifications have not been previously established, the POI shall require
the operator to fully substantiate the contractor's qualifications before granting
approval to the operator system.
D. Procurement. Operators should procure computer programs from
a reliable source. The computer programmers should be qualified in both education
and experience. The validity of the computer program should be validated by
aeronautical engineers and computer specialists.
E. Performance. All of the calculations required in the regulations
for the type of airplane involved (as discussed in
Volume 4, Chapter 3, Section 1) must
be performed, including en route and destination calculations.
F. Obtaining Data. For real-time systems, the operator's method
of obtaining data for a specific flight and for transmitting that data to and
from the individual performing the calculations must be shown to be accurate and timely.
G. Review. The POI or a designated inspector should review the
verification process conducted by the operator. Several runways at different
airports should be selected for verification with the AFM data. Short runways
with obstacles should be checked by manual calculation, particularly at airports
with higher temperatures and elevations.
1) The operator should be able to identify all of the obstacles
evaluated by the computer and the one selected as the limiting obstacle in each
case. The POI must be aware that under different temperature and weight conditions,
a different flap setting may be required, and different obstacles may be controlling.
The inspector should ensure that the operator has verified the limiting obstacle
under various conditions and flap settings.
2) The POI should contact the RFSD or the applicable Aircraft
Evaluation Group (AEG) through the RFSD for assistance when technical problems arise.
RESERVED. Paragraphs 4-552 through 4-570.