# Alt Calc

Alt Calc helps estimate holding and diversion status for alternate airports.

## <mark style="color:$warning;">Inputs</mark>

| Input              | Description                                          |
| ------------------ | ---------------------------------------------------- |
| Aircraft           | Selects default hold burn and reserve values.        |
| Hold burn          | Tonnes per hour used for holding calculations.       |
| Fuel at hold fix   | Fuel expected or actual at the hold fix.             |
| Extra / delay fuel | Additional fuel above the planned basis.             |
| Final reserve      | Reserve fuel to protect in calculations.             |
| Hold fix UTC       | Time used for live countdown and last-exit timing.   |
| Alternates         | Airport and OFP fuel requirement for each alternate. |

## <mark style="color:$warning;">OFP bridge</mark>

OFP Brief can send alternate information to Alt Calc. The transfer can include:

* Alternate airports.
* Alternate OFP fuel.
* Final reserve.
* Aircraft name.
* Estimated fuel at the hold fix.
* Hold fix time.

After loading, the pilot can override any calculation parameter.

## <mark style="color:$warning;">Outputs</mark>

Each alternate row can show:

* Required divert fuel.
* Holding fuel available after divert.
* Holding time remaining.
* Last exit UTC.
* Status color and label.

## <mark style="color:$warning;">Events and alarms</mark>

Status changes can trigger audio and banner alerts. The event log records status transitions and divert declarations for review during the session.


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