Old 8th Jan 2014, 08:42
  #84 (permalink)  
Join Date: May 2003
Location: Europe
Posts: 864
One of the problems with this subject is that most regulations are written in the language of visibility – where visibility is defined in the context of an object (from ICAO Annex 2):

Visibility. Visibility for aeronautical purposes is the greater of:
(a) the greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background;

(b) the greatest distance at which lights in the vicinity of 1 000 candelas can be seen and identified against an unlit background.
When the subject is more associated with flight in a 'usable cue environment' (or more correctly, 'in degraded visual conditions') – a far more complex issue.

Although the certification code contains a hook for addressing such issues:

27/29.141 The rotorcraft must--
(a) Except as specifically required in the applicable section meet the flight characteristics requirements of this subpart

(c) Have any additional characteristic required for night or instrument operation, if certification for those kinds of operation is requested. Requirements for helicopter instrument flight are contained in Appendix B of this Part.
it is unusual for any additional characteristics to be specified for ‘night flight’ - when it relies upon the visual cue environment for maintenance of stability/control.

For that reason, CASA might be well advised to refer to CAA Paper 2007/03 ‘Helicopter Flight in Degraded Visual Conditions’ - an extremely good treatise, dealing with this very subject, and which contains appropriate recommendations.

JimL is offline