# Weather & capacity

<p id="bkmrk-bad-weather-reduces">Bad weather reduces how many aircraft an airport can handle. This page explains which CDM tools help, and when.</p>

<h2 id="bkmrk-first-check-demand">First: check demand</h2>
<p id="bkmrk-only-act-when-demand" class="callout info">Only use CDM measures when <strong>demand is higher than the reduced capacity</strong>. If traffic is light, bad weather alone is not a reason to regulate. Normal spacing, holding and coordination are enough.</p>
<p id="bkmrk-how-to-check-demand">Check the arrival and departure lists, or the CDM dashboard, for how many flights are expected per hour.</p>

<h2 id="bkmrk-departures-lvo">Departures: LVO rate</h2>
<p id="bkmrk-each-airport-has-an">Each airport has a normal and a low-visibility (LVO) departure rate. See <strong>Airport CDM data</strong>.</p>
<ul id="bkmrk-lvo-when">
<li>Use the LVO rate <strong>only when low-visibility procedures are in force</strong>.</li>
<li>Strong wind, gusts or a low cloud base alone do not mean LVO. If departures need extra spacing in those conditions, agree it with the master.</li>
</ul>

<h2 id="bkmrk-arrivals-regulation">Arrivals: arrival regulation</h2>
<p id="bkmrk-if-too-many-arrivals">If more arrivals are expected than the airport can take, an <strong>arrival regulation</strong> can be set on the CDM dashboard by lowering the airport's arrival rate for a time period. The CDM server then gives CTOTs to inbound flights.</p>
<p id="bkmrk-regulation-limits" class="callout warning">Arrival regulations only give CTOTs to flights departing from <strong>airports using CDM</strong>. Most long-haul traffic into BIKF (North America, much of Europe) departs from airports without CDM and will <strong>not</strong> be held on the ground.</p>
<p id="bkmrk-so-for-bikf">For BIKF this means an arrival regulation helps a little, but you will still need:</p>
<ul id="bkmrk-tactical-measures">
<li>Holding</li>
<li>Miles-in-trail or minutes-in-trail requested from the adjacent centre (Gander, Shanwick, Scottish, Bodø, etc.)</li>
<li>Speed control on arrival</li>
</ul>

<h2 id="bkmrk-example">Example: BIKF in strong crosswind</h2>
<p id="bkmrk-example-metar"><code>BIKF 14036G46KT 4000 DZRA BR OVC007 08/08 Q1005</code></p>
<ul id="bkmrk-example-points">
<li>Runway 10 is best for this wind (about 22 kt crosswind, gusting 28). Single runway operations.</li>
<li>A 700 ft cloud base with 4 km visibility is <strong>not</strong> LVO. Keep the normal departure rate.</li>
<li>Realistic arrival capacity is about 15–18 per hour instead of 26.</li>
<li>If fewer than about 15 arrivals per hour are expected: no regulation needed.</li>
<li>If arrivals start bunching above that: set an arrival regulation for BIKF of about 16 per hour on the dashboard for the affected period, and use holding or in-trail spacing for flights without CTOTs.</li>
</ul>

<h2 id="bkmrk-who-decides">Who decides?</h2>
<p id="bkmrk-who-decides-text">The CDM master, together with the APP/CTR controller, decides on LVO rates and arrival regulations. Inform the adjacent units when a regulation is in force.</p>