ETSO-C46a

MAXIMUM ALLOWABLE AIRSPEED INDICATOR SYSTEMS

1 Applicability

This ETSO gives the requirements which maximum allowable airspeed indicator systems that are manufactured on or after the date of this ETSO must meet in order to be identified with the applicable ETSO marking.

2 Procedures

- 2.1 General

Applicable procedures are detailed in CS-ETSO Subpart A.

- 2.2 Specific

None.

3 Technical Conditions

3.1 Basic

3.1.1 Minimum Performance Standard

Standards set forth in the attached ' Federal Aviation Administration Standard, Maximum Allowable Airspeed Indicator Systems ' as amended and supplemented by this ETSO:

- a. Tests procedures set forth in Society of Automotive Engineers (SAE) Aeronautical Standard (AS) 418A dated May 15, 1961, 'Maximum Allowable Airspeed Instrument, Reciprocating Engine Powered Aircraft', or SAE AS 437 dated April 15, 1963, 'Maximum Allowable A irspeed Instrument, Turbine Powered Aircraft', may be used for the purpose of showing compliance with related standards in this ETSO. However, environmental limits, or other limits, specified in these procedures must be adjusted if necessary to agree with those specified in this ETSO.

- b. Other test procedure may also be adequate and valid for the purpose.

- c. Where applicable, instead of the referenced FAA documents/paragraph the corresponding IR, CS or ETSO document/paragraph shall be used, when available.

3.1.2 Environmental Standard

As stated in the ' Federal Aviation Administration Standard, Maximum Allowable Airspeed Indicator Systems '.

3.1.3 Computer Software

None

- 3.2 Specific

None.

4 Marking

4.1 General

Marking is detailed in CS-ETSO Subpart A paragraph 1.2; in addition to the markings required by this paragraph, the instrument must be marked to indicate its range in knots and, if applicable, to identify the calibration employed to control the movement of the maximum allowable airspeed pointer in the Vmo and Mmo ranges, or to identify the particular aircraft type design on which the instrument is intended to be used.

- 4.2 Specific

None.

5 Availability of Referenced Document

See CS-ETSO Subpart A paragraph 3.

APPENDIX 1 TO ETSO-C46A -FEDERAL AVIATION ADMINISTRATION STANDARD, MAXIMUM ALLOWABLE AIRSPEED INDICATOR SYSTEMS

ED Decision 2003/10/RM

1.Purpose.

This document specifies minimum performance standards for pitot-static type, maximum allowable airspeed indicator systems which indicate continuously both indicated airspeed and maximum allowable airspeed.

2.Performance Requirements.

2.2.1 General

(a)Materials. Materials must be of a quality demonstrated to be suitable and dependable for use in aircraft instruments.

(b)Environmental conditions. The instrument must be capable of performing its intended function and not be adversely affected during or following prolonged exposure to the environmental conditions stated under section 3. Where optional environments conditions are set forth, the conditions selected must be declared as equipment limitations.

5.2.2 Detail requirements.

(a)Indicating means. Indicated airspeed and maximum allowable airspeed must be displayed in such a manner that the numerical values on the scale increase in a clockwise, left to right, or bottom to top direction.

(b)Case markings. The outlets in the case must be marked with 'P' for the pitot pressure connection, and with 'S' for the static pressure connection.

8.2.3 Design requirements.

(a)Adjustable settings. - (1) Maximum allowable airspeed pointer. An adjustable stop may be provided in the instrument for limiting the movement of the maximum allowable airspeed pointer. If included, the design of this adjustment must be such that it will not affect the indication of the pointer when the altitude pressure conditions and Mach Number setting are such that the limiting speed will be lower than that set by the adjustable stop. - (2) Mach Number. If a readily accessible means is provided for setting the instrument to any desired Mach Number, the value of the setting must be visible from the front of the instrument. When the instrument does not contain an external Mach Number setting adjustment, the value of the permanent Mach Number setting need not be visible from the front of the instrument.

(b)Visibility. The indicating means and all markings must be visible from any point within the frustum of a cone, the side of which makes an angle of at least 30° with the perpendicular to the dial and the small diameter of which is the aperture of the instrument case. The distance between the dial and the cover glass must be a practical minimum.

- (c) Calibration. - (1) Indicated air-speed pointer. The indicated airspeed pointer must indicate airspeed in accordance with the values contained in Table I. - (2) Maximum allowable airspeed pointer. The maximum allowable airspeed pointer must indicate maximum allowable airspeed values in the Vmo and Mmo limit ranges which - - (i) Follow the standard fundamental relationships of subsonic compressible flow gas dynamics which are stated in appendix A; or - (ii) Are adjusted to account for design factors that are characteristic of a particular aircraft type design such as, but not limited to, static source pressure error variations and variable speed limitations with altitude. - (d) Scale error. - (1) Instruments with permanent Mach Number setting. The indicated airspeed scale error and the maximum allowable airspeed scale error must not exceed the tolerances specified in Tables I and II, respectively, with the instrument set at its permanent Mach Number. - (2) Instruments with means for external Each Number setting adjustment. - (i) The indicated airspeed scale error must not exceed the tolerances specified in Table I with the instrument set at the lowest Mach number. - (ii) The maximum allowable airspeed scale error must not exceed the tolerances specified in Table II with the instrument set at the lowest Mach Number and at increasing Mach Number setting of not more than 0.10 to and including the maximum Mach Number. - (e) Hysteresis. The reading of the maximum allowable airspeed pointer first at 30,000 feet altitude and then at 10,000 feet altitude must not differ by more then 2 knots from the corresponding readings obtained for increasing altitudes during tests to assure the instrument complies with the scale error requirements of section 2.3(d)(2)(ii) of this TSO. - (f) After effect. To assure the instrument complies with the scale error requirements of section 2.3 (d) (2) (ii) of this TSO, the maximum allowable airspeed pointer must return to its original readings, corrected for any change in atmospheric pressure, within 3 knots, after not less than 1 or more than 5 minutes have elapsed following completion of performance tests. - (g) Friction. - (1) Maximum allowable airspeed pointer. The friction of the pointer must not produce an error exceeding 4 knots at each point indicated by an asterisk in Table II. - (2) Indicated airspeed pointer. The friction on the pointer must not produce an error exceeding 3 knots at each point indicated by an asterisk in Table I.

- (h) Leak. - (1) Case leak. When subjected to a static pressure differential of 15 inches of mercury between the inside and outside of the case, the internal pressure must not increase because of case leaks more than 0.05 inches of mercury at the end of 1 minute time following first application of the differential pressure. - (2) Airspeed diaphragm leak. There must not be any apparent movement of the indicated airspeed pointer for 1 minute after a sequence of events in which pressure sufficient to produce full scale deflection of the indicated airspeed pointer is applied to the pitot connection (static pressure connection open to atmosphere), the pressure source is stopped, and the connection tubing pinched.

3.Environmental Conditions.

- 3.1 Temperature. The instrument must perform its intended function over the range of ambient temperature from -30° to 50° C. With the instrument temperature stabilized at the limits of the range, the scale error must not exceed by more than 4.5 knots the tolerances specified in Tables I and II at the points marked with an asterisk. The instrument must not be adversely affected by exposure to the range of ambient temperature from -65° to 70° C.

- 3.2 Altitude. The instrument must perform its intended function and must not be adversely affected when operating in the pressure range from -1,000 feet and the maximum altitude of intended operation. The instrument must withstand an external case pressure of 50' Hg. absolute when installed properly and vented to an atmospheric pressure of approximately 29.92' Hg. absolute.

- 3.3 Vibration. The instrument must perform its intended function and must not be adversely affected when subjected to vibrations of the following characteristics:

- 3.4 Humidity. The instrument must perform its intended function and must not be adversely affected following exposure to the extreme condition of relative humidity in the range from 0 to 95 percent at a temperature of approximately 70° C. for a period of 10 hours.

4.Compliance Tests.

As evidence of compliance with this standard, the manufacturer must perform evaluation tests on proto- type instruments to demonstrate proper design, reliability in performance of its intended functions, and conformity with the performance standards of section 2. Tests must also be performed to demonstrate compliance with the environmental condition requirements specified in section 3.

5.Individual Performance Tests.

The manufacturer must conduct such tests as may be necessary on each instrument to assure that it will meet the minimum performance requirements of sections 2.3 (b) through 2.3 (h).

TABLE I

TABLE II

MEASA

VMO = CSO

VMO = Cso K - 1

Po

( 5C-soa K-1

k-1

APPENDIX A

Relationships For Calibrating Maximum Allowable Airspeed Pointer

- (1) For altitudes from sea level to altitude where - (2) For altitudes where MMO is limited factor:

Where: Vmo = Maximum allowable indicated airspeed in knots. Mmo= Maximum allowable mach. K = Ratio of specific heats=1.40 for air. Po = Pressure at sea level in inches of Hg. P = Ambient static pressure in inches of Hg. Cso = Speed of sound at sea level=661.48 knots. a = Density ratio at altitude. Vm = Maximum equivalent airspeed in knots