Client and Aircraft Information:
1. Client Name and Contact Details: Full name, address, contact numbers, and email address.
2. Aircraft Model and Registration: The specific model and tail number/registration of the aircraft serviced.
3. Date of Service: When the maintenance or repair work was completed.

Service Details:
1. Description of Services: Detailed breakdown of all maintenance tasks performed.
2. Hours of Labor: Number of hours worked and the labor rate charged.
3. Parts Used: List of all parts used, including part numbers and individual prices.
4. Additional Costs: Any additional costs, such as consumables, environmental fees, or tool rentals.

Pricing and Totals:
1. Subtotals: Separate subtotals for labor, parts, and additional costs.
2. Tax Calculation: Applicable sales tax based on the client’s location or where the service was performed.
3. Discounts or Credits: Any discounts provided or credits applied to the account.
4. Grand Total: The final amount due.

Payment Information:
1. Payment Terms: Such as due upon receipt, net 30 days, etc.
2. Accepted Payment Methods: Credit card, bank transfer, check, online payment portals, etc.
3. Late Payment Policies: Information on late payment fees or interest charges.

Additional Features:
1. Invoice Numbering: Unique and sequential invoice numbering for tracking and accounting purposes.
2. Notes Section: For any additional information or specific details relevant to the service or billing.
3. Service History Link: Reference to past services or open quotes for the client's review.
4. Branding: The maintenance company’s logo and branding on the invoice for a professional appearance.

System Functionalities:
1. Invoice Generation: Ability to automatically generate an invoice based on the entered service details.
2. Editing and Customization: Capability to edit invoices before finalization and send to clients.
3. Email Integration: Directly email invoices to clients from within the system.
4. PDF Export: Export invoices in PDF format for printing or saving offline.
5. Record Keeping: Maintain a record of all invoices generated for accounting and auditing purposes.
6. Payment Tracking: Keep track of which invoices have been paid, are due, or are overdue.
7. Reminders: Automated reminders for upcoming or overdue payments.
8. Security: Secure storage and handling of client and payment information.