Appendix K – Aerotowing of Sailplanes by Powered Sailplanes

CAA ORS9 Decision No. 1

For powered sailplanes used for aerotowing sailplanes and for the powered sailplane - sailplane aerotowing combination itself (hereafter the combination is referred to as the “aerotow“), the following requirements apply in addition to those in the main code: 

Notes: In the following the term “sailplane“ is used for aerotowed sailplanes as well as for aerotowed powered sailplanes. 

Aerotowing of more than one sailplane at a time needs further consideration and is not covered by this Appendix. 

1. Subpart B - FLIGHT 

1.1 (See AMC 22 Appendix K paragraph 1.1) 

1.2 CS 22.51 is applicable to the aerotow, except that 22.51(b)(2) is not applicable.
Compliance must be shown at 500 m above sea level. 

1.3 CS 22.65 is applicable to the aerotow. 
Compliance must be shown at 500 m above sea level. 

1.4 A new paragraph CS 22.77 is added: 

CS 22.77 AEROTOWING SPEEDS 

The minimum aerotowing speed and the best-rate-of-climb aerotowing speed must be determined by flight test. 

The minimum aerotowing speed must not be less than 1.3 V_S1 of either the powered sailplane or the aerotowed glider, whichever is the higher. 

1.5 CS 22.143, except the sideslip condition under subpara (a), is to be applied also to the aerotow. 

1.6 CS 22.151(c) and (d) are applicable to the aerotow. 

1.7 CS 22.207(b) is amended to read: 

(b) An audible artificial stall warning giving a clear and distinctive indication must be provided for the powered sailplane unless the stall warning is sufficiently clear and distinctive for the pilot, even under the additional work load when aerotowing. 

1.8 CS 22.207(d) does not apply to the aerotowing powered sailplane. 

1.9 CS 22.233(c) Powered sailplanes used for aerotowing sailplanes must be able to taxi and take-off without additional ground assistance. 

2. Subpart C - STRUCTURE 

2.1 CS 22.307 applies to the aerotow. 

2.2 CS 22.581 is amended to read: 

(a) It must be assumed that the aerotow initially is in stabilised level flight and that an aerotowing cable load of 50 daN (in the absence of a more rational analysis) acts at the aerotowing hook in the following directions: 

(1) rearwards in the direction of the fuselage longitudinal axis; 

(2) in the plane of symmetry rearwards and downwards at an angle of 20° to the fuselage longitudinal axis; 

(3) in the plane of symmetry rearwards and upwards at an angle of 40° to the fuselage longitudinal axis; and 

(4) rearwards and sidewards at an angle of 30° to the fuselage longitudinal axis. 

(b) It must be assumed that the aerotow is initially subjected to the same conditions as specified in CS 22.581(a) and the cable load due to surging suddenly increases to 1.0 Q_nom. 

Note: It is assumed that only textile aerotowing cables are used. 

(1) The resulting cable load increment must be balanced by linear and rotational inertia forces. These additional loads must be superimposed on those arising from the conditions of CS 22.581(a). 

(2) Q_nom is the rated ultimate strength of the weak links to be used for the aerotowed sailplanes and shown to be suitable in operation. 

2.3 CS 22.585 is amended to read: 

CS 22.585 Strength of the Aerotowing Hook Attachment

The aerotowing hook attachment must be designed to carry a limit load of 1.5 Q_nom as defined in CS 22.581(b) acting in the directions specified in CS 22.581. 

3. Subpart D - DESIGN AND CONSTRUCTION 

3.1 CS 22.689 applies also for the aerotow release system of the powered sailplane. 

3.2 CS 22.711 applies also for the aerotowing powered sailplane and is amended by adding paragraphs (h) and (i): 

(h) Release mechanisms for aerotowing sailplanes must be installed so that there is no interference between the aerotow rope and any control surface throughout their full angular movement, with the aerotowed sailplane in any position as defined in CS 22.581(a). 

(i) The release mechanism of the aerotowing powered sailplane must be suitably protected against general degradation caused by mud and dirt, etc.

(j) It must be possible for the pilot to visually check the aerotow cable situation. 

3.3 CS 22.713(c) is applicable to the release mechanism of the aerotowing powered sailplane. 

3.4 CS 22.780 is amended by adding the following requirement: 

Aerotowing cable release and throttle must be located and arranged to be capable of operation by the same hand. 

3.5 A Note is added: 

The requirements in Appendix K do not constitute all the requirements necessary to cover the installation of cable retracting devices. Compliance with further requirements may become necessary. 

4. Subpart E - POWERPLANT INSTALLATION 

4.1 A new paragraph CS 22.991 is added: 

CS 22.991 Fuel Pumps 

(a) If for the purpose of CS 22.951 a fuel pump is required for proper engine operation, an emergency pump must be provided to immediately supply fuel if the main pump fails. The power supply for the emergency pump must be independent of the power supply for the main pump. 

(b) If both the normal pump and the emergency pump operate continuously, a means or a procedure must be provided to indicate failure of either pump. 

(c) The operation of any fuel pump may not affect the engine operation so as to create a hazard regardless of the engine power setting or the functioning of the other fuel pump. 

4.2 CS 22.1047 must be applied to the aerotow. 

5. Subpart F - EQUIPMENT 

5.1 CS 22.1305(e) is amended to read: 

(e) a cylinder head temperature indicator or an indicator for the critical temperature determined in the cooling test. 

5.2 CS 22.1307 is amended by adding the following sentence: 

- An easily removable rear-view mirror of sufficient strength and rigidity must be attached and so located that the pilot, when seated with the seat belts fastened, has full and unobstructed view of the aerotowed sailplane in any position as defined in CS 22.581(a). It must be possible to permanently observe the aerotowed sailplane without other pilot’s tasks being affected and without major turning movements of the head. 

- An Aerotow rope as specified by the applicant. 

6. Subpart G - OPERATING LIMITATIONS AND INFORMATION 

Note: This information should normally be furnished under Section 9 of the Flight Manual. 

6.1 CS 22.1529 applies to powered sailplanes equipped for aerotowing. 

6.2 CS 22.1583 is amended by adding the following paragraph (k): 

 (k)     Aerotowing of sailplanes

The following information concerning aerotowing of sailplanes must be furnished:

(1) Maximum weight of the powered sailplane (if different from the value under (b)(1))

(2) Maximum weight of the aerotowed sailplanes

(3) Maximum weight of the combination powered sailplane and sailplane

(4) The minimum value for the maximum allowable aerotow speed of the aerotowed sailplane (V_T)

(5) Information that the powered sailplane shall lift off only after lift-off of the aerotowed sailplane

(6) Rated ultimate strength for the weak link to be used for the aerotowing cable.

(7) The specification of the aerotow rope (length, material, weak link) 

6.3 As far as applicable for the intended purpose, CS 22.1585 must be applied to the aerotow. In addition, the minimum aerotowing speed and the best-rate-of-climb speed for the aerotow must be furnished. Furthermore, sailplane types whose relevant characteristics are comparable to those of the types used in the flight tests must be furnished as examples. 

6.4 CS 22.1587(c) must be applied to the aerotow and is amended by the following requirements: 

In addition, information about the degradation of performance in take-off distance due to long grass, rain drops or contamination of the wing (leading edge), as specified by the applicant, must be furnished.