Shamal dust and a forecast below VFR minima

The flight cannot be planned as VFR on this forecast, and the SIGMET settles it.

• The reported visibility at departure is 4,000 m, below the 5 km minimum for the airspace, with a temporary condition of 1,500 m. A temporary group is not a licence to assume it will not happen during your flight window; it is a statement that the visibility will drop to that value at times in the forecast period, and your departure and climb-out fall inside that period.
• The destination is forecast at 5,000 m, exactly at the minimum, with temporary 2,000 m. With no margin at either end and a 1:20 flight, there is no point on the route where you can count on VMC.
• The SIGMET for a severe duststorm west of the route is directly relevant: you are flying west. A SIGMET is not background information.
• The pressure rise of 3 hPa per hour with a 12 °C temperature–dewpoint spread and strengthening gusty wind indicates strong cold advection and an unstable, dusty airmass that is likely to keep the dust aloft for hours, not minutes.
• The gust spread (24G38) is significant for handling at both ends and for any crosswind, but the visibility is the deciding factor.
• Correct decision: no-go, or delay and re-brief later against a fresh TAF and observation with a genuine margin above 5 km at both ends and along the route.

Treat this as a loss of VMC and act immediately, not incrementally.

• Do not scud-run. Descending to stay under the dust and maintain ground contact is how VFR flights become controlled-flight-into-terrain accidents, especially over flat featureless desert with no relief cues.
• Fly the aeroplane first: wings level, a positive pitch attitude, and a 180° turn back towards the better visibility you came from. Do not turn so steeply that you lose the horizon or load the aircraft unnecessarily.
• Navigate by reference to the GPS track, the heading indicator, the altimeter and the VSI rather than by outside features. Fix a minimum safe altitude for the area before you need it and do not descend below it.
• Declare it: call ATC, state that VMC cannot be maintained, request vectors to the nearest aerodrome and any known visibility reports. If you hold no instrument rating, say so - ATC will help, but they cannot fly the aircraft.
• Beware the somatogravic and other vestibular illusions that dust, haze and a missing horizon create during acceleration and turns; believe the instruments.
• Land at the first suitable aerodrome and wait. Dust this dense behind a cold front will not clear in ten minutes, so the decision is diversion, not patience.

Dust attacks the air data system, the engine and the pilot.

• Pitot-static system: dust can enter the pitot tube and the static ports. A blocked pitot leaves the airspeed indicator behaving like an altimeter; a blocked static source makes the altimeter, the airspeed indicator and the VSI all unreliable together. Switch pitot heat on, use the GPS groundspeed as a cross-check, and fly attitude and power if the airspeed becomes suspect.
• Engine: the dry paper air filter loads up. Expect a progressive loss of power and a possible enrichment problem; use carburettor heat only as the POH permits, and lean appropriately. The filter must be checked and replaced after flight.
• Visibility on approach: dust cuts slant visibility far more than reported surface visibility. A reported 2,000 m horizontal visibility may leave you unable to see the runway from a 3° final. Brief a late go-around and do not force the landing.
• Wind: gust spread of 15–20 kt close to the ground means significant low-level turbulence and a real possibility of windshear on final; carry extra approach speed and be ready to go around.
• Airframe: dust abrades windscreens and leading edges and gets into hinges and the cabin. Plan an inspection and a wash after landing.
• Pilot: a hazy, dusty, featureless visual scene is a classic setup for spatial disorientation in the turn. Keep the instrument cross-check disciplined.