Why PHASE

An investigation report holds facts, parameters, communications, witness accounts and recommendations. It tells the sequence of events. That account is necessary. It is not enough to understand how the situation changed.

PHASE starts from there. Its reference line: make flight dynamics visible, to better understand, debrief and train.

The time the reader cannot see

A report is organised by theme: weather, aircraft, crew, organisation. The same moment is spread across several chapters and never seen whole.

So the reader rebuilds the timeline in their head, one sentence after another. That is exactly the memory work the crew could not do under pressure.

A report answers the question “what caused the event?”. PHASE asks different questions:

• for how long?
• in what order?
• what was happening at the same time?

Dynamic complexity

What makes a flight hard is not how many things it contains. It is how they behave over time.

A threat can be present long before it has any effect. A deviation can build up gradually. An action produces its consequence later, and somewhere else. Each correction changes the conditions for the next one. Several things are active at once.

This is dynamic complexity. A photograph shows a state. A narrative shows a series of states, one sentence after the next. Neither shows what connects those states: what lasts, what overlaps, what comes back. As long as time stays invisible, that complexity can be told. It cannot be seen.

The time it takes to process

A piece of information reaches the flight deck: a warning, a clearance, a speed deviation. It is available. It is picked up, or it is not. If it is, it gets processed, at one level or another: a simple correction, or a decision that requires understanding the situation and talking it through. Then a response comes back to the aircraft and changes its state, or doesn’t.

Each of these steps takes time. Not much, but never none. That is often where a case is decided: a signal has been available for twenty seconds, and nothing above it has moved.

PHASE makes that time visible. On the chart, time runs horizontally. Vertically, position shows how far the information has travelled through processing: threat, aircraft state, error, competencies, internal conditions. Reading a chart explains both axes, and the available signal demo shows such a delay.

Diagram versus text

Two representations can hold the same information and still demand different work. Text is sequential: the reader has to work out the link between two sentences. A diagram is indexed by position: what lines up or overlaps can be seen directly. This is a long-standing finding in cognitive psychology (Larkin and Simon, 1987).

The questions a flight raises are precisely the ones that position on a plane makes visible: what came first, what happened at the same time, what lasted, what came back.

A chart is not a replay. The past stays in view. The reader moves through it at their own pace and decides where to look.

From event to understanding

PHASE breaks the narrative down into time-stamped facts. Each fact is placed in time, then in one of the chart’s ten strata. Each shape opens a record that states where the fact comes from and how solid it is.

Three principles guide the work:

• place before explaining: facts go on the time axis before they are classified;
• distinguish before linking: a sequence does not become a cause;
• trace before concluding: every element keeps its source and its status.

PHASE is not only interested in what failed. Most of a crew’s activity is made up of countermeasures. A chart also shows what protected, what recovered, what was still holding.

From understanding to training

A finished case then serves several purposes. It supports debriefing, where the discussion is about an object, not a person. It supports training, where each EBT/CBTA competency is shown at the moment it comes into play. It supports flight safety, where flight data and the pilot’s report are read on the same axis. Uses covers each in turn.

Time also changes the conversation. “The checklist was omitted” becomes “at that moment, three tasks were running”. “You should have…” becomes “look at what was active there”.

Where PHASE comes from

PHASE comes from the field: flight instruction, pilot training, event analysis. A first formalisation, then called OOPS, was presented at HCI-Aero 2016, Paris, 14–16 September (Charrier, Nicolas, Charron; not published in the proceedings; HAL hal-02468273). According to the 2016 paper, the model was used in training for two years and was employed by trainers with 240 French Air Force instructor pilots.

Today’s method keeps its core: input through perception, output through action, and the question “how far ahead of the aircraft is the crew?”. It adds a visual grammar, status-based coding and a record behind every object.

What PHASE is worth for understanding, debriefing and training is still to be measured. The Status and limits page sets this out in detail.