Night IFR into a Non-Towered Field with Deteriorating Weather
You are PIC of a twin-engine turboprop on an IFR flight plan at FL180, 45 minutes from destination, a non-towered airport with one runway (09/27, 1,400 m, no ILS, only RNAV approaches to both ends). Forecast was 3,000 ft broken, 6 km visibility. ATIS now reports 400 ft overcast, 1,200 m visibility, wind 090/12 kt, temperature 2 °C, dew point 1 °C. Your alternate is 60 NM away with an ILS and reported 1,000 ft broken, 8 km. Minimum fuel at destination is 25 minutes holding; you have 55 minutes of fuel above alternate reserves. The RNAV 27 minima are 520 ft and 1,600 m. Sunset was 20 minutes ago; you are night current but the last three approaches were in daylight. The aerodrome has no weather observer after 18:00 local, and the ATIS is automated.
1. Evaluate whether you may legally and safely continue to the destination, considering the approach minima, the automated weather, and your night recency.
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Two independent gates must both pass: legality and prudent airmanship.
Legality: The reported ceiling (400 ft) and visibility (1,200 m) are below the RNAV 27 minima (520 ft / 1,600 m). Under IFR you may not commence an approach unless the aerodrome is at or above minima; you may hold and wait, but you cannot plan to land. Because the weather is automated and unmonitored, there is no human observer to issue a trend or a special report; automated systems can report a cloud base that does not reflect the actual layer over the threshold, so the report is a snapshot, not a guarantee.
Recency: Night currency is satisfied, but currency is not proficiency. Three daylight approaches do not prepare you for a circling-free straight-in at night into an unlit, non-towered field with a 1,400 m runway and no centreline lighting.
Decision: Do not press on hoping for improvement. Divert to the alternate while you still have fuel to do so comfortably, or hold only if a genuine trend and fuel margin exist. The temperature/dew point spread of 1 °C also warns of fog and possible airframe icing in cloud.
2. The temperature/dew point spread is 1 °C and you are in cloud at +2 °C. What icing and visibility hazards should drive your decision, and how do they interact with the approach?
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A 1 °C spread at +2 °C means the air is close to saturation. Two consequences follow.
First, fog or very low stratus can form or thicken rapidly, especially after sunset when radiative cooling continues. The automated ATIS may lag the real conditions by several minutes, so the actual visibility over the threshold could be worse than 1,200 m.
Second, at +2 °C in visible moisture you are in the classic icing band. Supercooled droplets can accrete on the airframe, pitot system and antennas. Icing increases stall speed, reduces climb performance and can block the static source, corrupting your altimetry and airspeed indications just when you need them for the approach.
Interaction: A contaminated airframe raises your approach speed and landing distance on a 1,400 m runway, and a blocked static port can make the altimeter read high, tempting you below minima. The correct response is to exit icing conditions (climb or descend to a temperature band clear of visible moisture), use pitot heat and anti-ice continuously, and treat the destination as unsuitable until a monitored report shows a clear improving trend.
3. If you elect to divert, what should your diversion briefing include, and what would you tell ATC?
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Brief the diversion as a mini flight plan:
- Fuel: confirm fuel over the alternate plus 45 minutes, and note the point of no return if you hold.
- Route: the cleared route or a direct routing if ATC can offer one; terrain and minimum safe altitude along the way.
- Weather at the alternate: 1,000 ft broken and 8 km is comfortably above the ILS minima, but check the trend and the alternate's own forecast validity period.
- Approach: brief the ILS fully, including missed-approach instructions, before you need them.
- Contingency: if the alternate deteriorates, identify a second suitable aerodrome now.
Call ATC early: state your position, that you are diverting to the alternate due to weather below minima at destination, request the revised clearance and, if useful, a higher or lower level to exit icing. Early communication preserves options; waiting until fuel is tight removes them.