The alertType is the type of event to trigger an alert on and defaults to EN_ROUTE.
Options are: EN_ROUTE, LANDED, DIVERTED, CANCELLED, PRE_DEPARTURE_STATUS, PRE_ARRIVAL_STATUS, DEPARTURE_DELAY, ARRIVAL_DELAY, TIME_ADJUSTMENT, DEPARTURE_GATE, ARRIVAL_GATE, GATE_ADJUSTMENT, EQUIPMENT_ADJUSTMENT, BAGGAGE.
The alertType in the simulated alert is restricted to the list given. The list items are the possible events someone could see on a delivery. For example, arrDelayAllowRunway is clarification/refinement of what types of changes the arrDelay subscription would find relevant (e.g. runway delays would trigger events).
If you'd like to test arrival delays, you would ask for an ARRIVAL_DELAY simulated event. Whether you'd get the real event on a runway delay would depend on if you specify the arrDelayAllowRunway subscription.