010 Air Law topic guide
Alerting Phases: INCERFA, ALERFA, DETRESFA
When an aircraft's safety becomes doubtful, the air traffic and search and rescue system does not jump straight to launching a rescue. It escalates through three named alerting phases: INCERFA for uncertainty, ALERFA for alert, and DETRESFA for distress, each describing a different level of confidence that something has actually gone wrong. A phase is a trigger for a defined set of actions by air traffic services and rescue coordination units, not a label the pilot applies to their own situation.
The exam usually gives a short scenario, a flight that has missed a position report, one that cannot be raised by radio, one that has vanished from radar moments after a garbled call, and asks which phase fits. The reliable approach is separating genuine uncertainty from a specific, credible indication of danger, because that split is exactly where the three phases divide.
What triggers each phase
INCERFA, the uncertainty phase, exists when doubt arises about the safety of an aircraft and its occupants, typically because it has failed to communicate as expected or has not arrived within a reasonable time of its last position report, but nothing yet points to a specific danger.
ALERFA, the alert phase, exists when apprehension is justified: for example, repeated attempts to establish contact have failed, or an aircraft has failed to arrive after communications are not established within the prescribed intervals following its estimated time, without any direct evidence of grave danger.
DETRESFA, the distress phase, exists when there is reasonable certainty that the aircraft and its occupants are threatened by grave and imminent danger and need immediate help, for example a definite distress call, confirmed fuel exhaustion, or an aircraft that disappears from radar and stays unreachable once the alert phase has run its course.
Who declares a phase, and how escalation works
A pilot's own distress call can supply the evidence, but the phase itself is declared by the responsible air traffic services unit or rescue coordination centre acting on the information available, never simply asserted by the pilot. Escalation does not have to pass through all three steps in order: if the first information received is already a definite distress call or a wreckage sighting, the appropriate authority can declare DETRESFA immediately, without first working through INCERFA and ALERFA. Equally, if an aircraft that triggered ALERFA later re-establishes contact and confirms it is safe, the phase is stood down rather than left running.
Why this pairs with radio failure procedures
The classic trigger for INCERFA or ALERFA is precisely a loss of communication, so a stem about alerting phases is frequently built on the same facts as an IFR radio failure question. Recognising whether a stem is asking what the pilot should do about lost communications, a radio failure procedure, or what phase the ground service would declare, an alerting phase question, is itself worth marks before any of the specific detail matters.
Worked example
Worked example: matching the scenario to the phase
Not quite. The correct answer is B.
Correct answer: B
- A. Uncertainty fits a single missed report or an early, unconfirmed delay. Here contact has already failed repeatedly and the arrival is genuinely overdue, which is a stronger signal than plain uncertainty.
- B. Correct. Apprehension is now justified: repeated failed contact combined with a real overdue arrival, without direct evidence of grave and imminent danger, is exactly the alert phase.
- C. Distress needs reasonable certainty of grave and imminent danger, such as a confirmed distress call or wreckage. Nothing in the stem confirms actual danger, only prolonged silence, so distress overstates the evidence.
- D. The pilot does not need to declare anything for a phase to exist. Alerting phases are raised by air traffic services and rescue coordination units from the information available to them, not from a pilot declaration.
Step by step
- Identify what evidence exists: failed radio contact, repeated attempts, and a genuinely overdue arrival, but nothing confirming actual danger.
- Rule out INCERFA: that phase covers doubt from a single missed contact or an early delay, and this stem already goes beyond that with repeated failures and a real overdue arrival.
- Rule out DETRESFA: distress needs reasonable certainty of grave and imminent danger, which nothing here confirms.
- What remains is ALERFA, the phase for justified apprehension without confirmed danger.
- Note that the phase is raised by air traffic services or the rescue coordination centre, never by the pilot declaring it.
Common mistakes
Jumping straight to DETRESFA whenever an aircraft goes quiet
Distress requires an actual indication of grave and imminent danger, not just silence. Overreading uncertainty as automatic distress wastes an easy mark on a scenario built to test ALERFA instead.
Assuming the pilot must declare the phase
A common distractor rests on this exact misunderstanding, that no phase can exist without a distress call. It is air traffic services and rescue coordination units that declare a phase, from whatever information they hold at the time.
Assuming the three phases must run strictly in sequence
A stem describing a definite crash report or an unambiguous distress call, with no prior loss of contact, can jump directly to DETRESFA. Expecting INCERFA and ALERFA to appear first leads to picking the wrong phase or an unnecessary "no phase applies" trap.
Related topic guides
Practise Air Law the way the exam asks it.
SkyStudy turns Alerting Phases: INCERFA, ALERFA, DETRESFA and every other Air Law topic into exam-style practice questions with explanations, spaced repetition, and timed mock exams. Free to start.
Important information
This page is general educational information for student pilots and may be out of date.
Aviation rules, training requirements, costs, medical standards, and exam details change over time and vary by country, authority, and training organisation, so details here may no longer be current or may differ in your case.
Always confirm the current details with your approved training organisation (ATO) and national aviation authority before relying on them.
SkyStudy is an independent study aid, is not affiliated with EASA or any aviation authority, and does not guarantee any exam or licence outcome.
Last reviewed July 2026