CS HPT-DSN.F.660 Visual approach slope indicator

(a)Applicability: Where provided at a heliport, a visual slope indicator system should provide information on the approach angle necessary to maintain a safe height over obstacles on the approach to a heliport.

(b)The standard visual approach slope indicator systems for helicopter operations should consist of the following:

(1)PAPI (precision approach path indicator) and APAPI (abbreviated precision approach path indicator) systems conforming to the specifications contained in CS ADR-DSN.M.645 and CS ADR-DSN.M.650, except that the angular size of the on-slope sector of the systems should be increased to 45 minutes of arc; or

(2)HAPI (helicopter approach path indicator) system conforming to the specifications in paragraphs (d) to (g) below.

(c)Location:

(1)A visual approach slope indicator should be located such that a helicopter is guided to the desired position within the FATO and so as to avoid dazzling the pilot during final approach and landing.

(2)The light unit(s) should be mounted as low as possible.

(d)Characteristics of the HAPI signal format:

(1)The signal format of the HAPI should include four discrete signal sectors, providing an ‘above slope’, an ‘on slope’, a ‘slightly below’ and a ‘below slope’ signal.

(2)The signal format of the HAPI should be as shown in Figure F-11, Illustrations A and B.

(3)The signal repetition rate of the flashing sector of the HAPI should be at least 2 Hz.

(4)The on-to-off ratio of pulsing signals of the HAPI should be 1 to 1, and the modulation depth should be at least 80 per cent.

(5)The angular size of the ‘on-slope’ sector of the HAPI should be 45 minutes of arc.

(6)The angular size of the ‘slightly below’ sector of the HAPI should be 15 minutes of arc.

Figure F-11. HAPI signal format

(e)Light distribution:

(1)The light intensity distribution of the HAPI in red and green colours should be as shown in Figure F-9, Illustration 3.

(2)The colour transition of the HAPI in the vertical plane should be such as to appear to an observer at a distance of not less than 300 m to occur within a vertical angle of not more than three minutes of arc.

(3)The transmission factor of a red or green filter should be not less than 15 per cent at the maximum intensity setting.

(4)At full intensity, the red light of the HAPI should have a Y-coordinate not exceeding 0.320, and the green light should be within the boundaries specified in CS ADR-DSN.U.930(b).

(5)A suitable intensity control should be provided so as to allow adjustment to meet the prevailing conditions and to avoid dazzling the pilot during approach and landing.

(f)Approach slope and elevation setting:

(1)A HAPI system should be capable of adjustment in elevation at any desired angle between 1 degree and 12 degrees above the horizontal with an accuracy of ± 5 minutes of arc.

(2)The angle of elevation setting of a HAPI should be such that during an approach, the pilot of a helicopter observing the upper boundary of the ‘below slope’ signal would clear all objects in the approach area by a safe margin.

(g)Characteristics of the light unit:

(1)The system should be so designed that:

(i)in the event the vertical misalignment of a unit exceeds ± 0.5 degrees (± 30 minutes), the system should switch off automatically; and

(ii)if the flashing mechanism fails, no light is emitted in the failed flashing sector(s).

(2)The light unit of the HAPI should be so designed that deposits of condensation, ice, dirt, etc. on optically transmitting or reflecting surfaces would interfere to the least possible extent with the light signal and should not cause spurious or false signals to be generated.

(h)Obstacle protection surface (applicable to PAPI, APAPI and HAPI):

(1)An obstacle protection surface should be established when it is intended to provide a visual approach slope indicator system.

(2)The characteristics of the obstacle protection surface, i.e. origin, divergence, length and slope, should correspond to those specified in the relevant column of Table F-1 and in Figure F-10.

(3)New objects or extensions of existing objects should not be permitted above an obstacle protection surface except when the new object or extension would be shielded by an existing immovable object.

(4)Existing objects above an obstacle protection surface should be removed except when the object is shielded by an existing immovable object, or when after a safety assessment, it is determined that the object would not adversely affect the safety of operations of helicopters.

(5)Where a safety assessment indicates that an existing object extending above an obstacle protection surface could adversely affect the safety of operations of helicopters, one or more of the following measures should be taken:

(i)suitably raise the approach slope of the system;

(ii)reduce the azimuth spread of the system so that the object is outside the confines of the beam;

(iii)displace the axis of the system and its associated obstacle protection surface by no more than 5 degrees;

(iv)suitably displace the FATO; and

(v)install a visual alignment guidance system.