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Cloud

Cloud formation in itself is not generally a concern for operating into and out of airports, subject to the type of cloud (note that cumulonimbus or CB clouds are often associated with thunderstorms - en route and at airports - both of which are discussed below). Low cloud on the approach path may be a concern for meeting minimum conditions either for a visual or instrument approach. The IOC through its meteorological function will be alerted to conditions such as forecast low cloud, as will the operating crews of the flights.

IOC response

The circumstances are similar but not as challenging as for a fog condition. Whereas fog can be quite unpredictable, cloud formation and dissipation are less so. Often, cloud base height above the airfield fluctuates and the thinking may well be to consider dispatching a flight with sufficient fuel for holding at or near the destination airport until conditions permit an approach and landing. Should low cloud obscure one approach to, or one end of, the runway, subject to the wind conditions and air traffic there may be an opportunity for an approach from the opposite end. Sometimes АТС may instigate this or the operating crew request, but this may also be an opportunity for astute IOC Controllers.

Information required in this instance is as follows:

  • a) Between the IOC (involving the Meteorology area), Operating Captains and perhaps the port staff, what is the perceived risk of operating on time? That is, would the aircraft be expected to land without too much difficulty (i.e., extensive holding or missed approaches)?
  • b) How much fuel is the aircraft carrying?
  • c) What alternates have been planned?
  • d) How long can the aircraft hold before diverting?

The options also are similar:

  • a) If the cloud base is becoming lower, what are the wind conditions like? Is there a chance of executing an approach from the opposite end (subject to instrument procedures and АТС requirements)?
  • b) If not, should the flight depart on schedule?
  • c) If the cloud base is fluctuating, should the flight depart on schedule?

The thinking processes will be informed by meteorological and АТС advice and also take into account crew assessment of the conditions, and local airport knowledge. The success or otherwise of recent or current attempts to land also help to inform the picture.

Wind

Wind affects operations in several ways. In flight, strong headwinds may add extensive time to planned flight durations. If the flight plan provides for the forecast headwinds, then sufficient fuel for the flight (including all necessary reserves) will be carried and the flight can operate normally. However, if winds greatly exceed the forecast wind, an aircraft already in flight will likely have to divert into an en-route port to uplift additional fuel. In contrast, strong tailwinds shorten flight time, which saves time and hence fuel (maybe even crew duty time) but brings about a different consideration. If, for example, a flight is scheduled to arrive at a port at the end of a curfew (e.g., an overnight flight scheduled to arrive at 0600), a significantly shorter flight time may mean that the flight either has to be slowed significantly (which leads to inefficiency and additional fuel burn) or as is commonly done, delayed at the departure port to avoid arriving during the curfew period.

Of more significance is the presence of strong, changeable winds, and in particular wind shear, around airports, making approaches more challenging and in some cases, dangerous. Where the runway configurations (and АТС procedures) allow, aircraft will normally take off and land into the prevailing wind. The limits applying to aircraft taking off and landing in cross-winds operations are constrained according to the aircraft manufacturer’s certification. Thus, operations into single-runway airports that are experiencing strong cross-winds may not be possible. Even at large major airports, and despite normal АТС procedures enabling the use of multi-directional runways on most occasions, strong winds from a given direction may reduce the availability of some runways, thereby severely limiting traffic movements at the airport resulting in traffic build-up, congestion and delays to inbound flights.

IOC response

Cross-wind conditions are a particular cause for concern within the IOC. If adverse wind conditions at specific airports are expected to disrupt a flight for the reasons given above, the IOC together with the Pilot in Command will consider several options, each of which has a number of considerations:

  • a) If the strong wind conditions are likely to dissipate before arrival, departure should be on time.
  • b) If conditions are expected to persist until about the time of arrival, can additional fuel be uplifted to enable a period of holding?
  • c) What alternate(s) is nominated?
  • d) How much additional fuel must be carried taking into account the alternate(s) required?
  • e) Will this additional fuel result in a payload offload?
  • f) If conditions are expected to last well beyond arrival time, should the aircraft even be dispatched with little probability of being able to land? Is there another (unaffected) airport lying close to the original destination such that passengers could be road transported between the two locations?

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