Craft Lifecycle

Every craft in ATC follows a defined lifecycle — a sequence of states from creation to completion (or failure). Understanding the lifecycle is key to understanding how ATC orchestrates changes.

States

State	Terminal	Description
Taxiing	No	Craft initialized — branch created, pilots assigned, cargo and flight plan defined
InFlight	No	Pilots actively implementing, navigating vectors in order
LandingChecklist	No	All vectors passed. Pilot runs validation checks
GoAround	No	Landing checklist failed. Pilot addresses failures before re-attempt
ClearedToLand	No	Checklist passed, tower granted clearance. Craft is in merge queue
Landed	Yes	Branch merged into main. Done.
Emergency	No	Pilot declared an emergency after repeated failures
ReturnToOrigin	Yes	Craft sent back to design stage for re-evaluation. Done.

State Diagram

                    ┌─────────────────────────────────────────┐
                    │                                         │
                    ▼                                         │
  ┌──────────┐   ┌──────────┐   ┌─────────────────┐   ┌───────────┐
  │ Taxiing  │──▶│ InFlight │──▶│ LandingChecklist │──▶│ GoAround  │
  └──────────┘   └──────────┘   └─────────────────┘   └───────────┘
                    │  ▲              │                      │
                    │  │              │                      │
                    │  └──────────────┘                      │
                    │  (vector passed)        ┌──────────────┘
                    │                         │
                    │                         ▼
                    │              ┌─────────────────┐   ┌──────────────────┐
                    │              │    Emergency     │──▶│ ReturnToOrigin   │
                    │              └─────────────────┘   │    (terminal)    │
                    │                                    └──────────────────┘
                    │
                    ▼
            ┌───────────────┐   ┌──────────┐
            │ ClearedToLand │──▶│  Landed  │
            └───────────────┘   │(terminal)│
                                └──────────┘

Transitions

#	From	To	Trigger	Preconditions
1	Taxiing	InFlight	Pilot begins implementation	Captain, cargo, and flight plan assigned
2	InFlight	InFlight	Pilot passes a vector and reports to ATC	Next vector in flight plan sequence
3	InFlight	LandingChecklist	Pilot begins validation checks	All vectors passed and reported
4	LandingChecklist	ClearedToLand	All checks pass; tower grants clearance	All checklist items pass
5	LandingChecklist	GoAround	One or more checks fail	At least one checklist item failed
6	GoAround	LandingChecklist	Pilot re-attempts after fixing failures	Pilot has addressed failure(s)
7	GoAround	Emergency	Repeated failures or pilot escalates	Captain decision
8	ClearedToLand	Landed	Tower merges branch into main	Branch up to date with main
9	Emergency	ReturnToOrigin	Craft sent back to design with black box	Emergency declaration recorded

Terminal States

Two states are terminal — no transitions out are permitted:

• Landed: The craft's branch has been merged into main. The change is complete.
• ReturnToOrigin: The craft has been sent back to the design stage. The origin airport will decide whether to re-plan, re-scope, or abandon.

The Happy Path

The most common lifecycle follows this sequence:

1. Taxiing — craft is set up with callsign, cargo, pilots, and flight plan
2. InFlight — pilots implement the change, passing vectors one by one
3. LandingChecklist — all vectors done, validation checks run
4. ClearedToLand — everything passes, tower grants clearance
5. Landed — branch merged, craft complete

The Go-Around Loop

If the landing checklist fails, the craft enters GoAround. The pilot fixes the issues and re-enters LandingChecklist. This loop can repeat multiple times. If the pilot can't resolve the failures after repeated attempts, the captain may escalate to Emergency.

Rules

• RULE-LIFE-1: A craft must begin in the Taxiing state.
• RULE-LIFE-2: Only the transitions listed above are valid. Any unlisted transition is illegal.
• RULE-LIFE-3: Taxiing to InFlight requires a captain, cargo, and flight plan to be assigned.
• RULE-LIFE-4: InFlight to LandingChecklist requires all vectors to be passed and reported.
• RULE-LIFE-5: LandingChecklist to ClearedToLand requires all checklist items to pass and the tower to grant clearance.
• RULE-LIFE-6: ClearedToLand to Landed requires the tower to verify the branch is up to date with main and execute the merge.
• RULE-LIFE-7: Emergency to ReturnToOrigin requires an EmergencyDeclaration entry in the black box.
• RULE-LIFE-8: Landed and ReturnToOrigin are terminal states. No transitions out are permitted.

Related Concepts

• Crafts — the entity that moves through this lifecycle
• Vectors & Flight Plans — drive the InFlight phase
• Landing Checklist — the validation gate before clearance
• Emergency Declaration — the escape hatch
• Tower — manages ClearedToLand → Landed