Maintenance intervals

What it is

Every maintenance item has an interval type that decides how Syndik8 tracks “when is it next due?”. Interval types fall into two families:

Usage-based: driven by something the syndicate records each flight.

Hours: a number of hours flown or a number of hours on the meter.

Calendar-based: driven by elapsed time.

Day: any cadence expressed as a number of days (e.g. 7 days, 30 days, 365 days).
Month: a number of calendar months (e.g. 4 months for an oil change, 6 months for a half-yearly check).
Year: a number of calendar years (e.g. 1 year for an annual or an ARC).

A usage-based item also names the measure it counts against. “Every 50 hours” is not a complete instruction on its own: 50 hours of flying and 50 hours on a Hobbs meter are different amounts of aircraft, because the Hobbs keeps running while you taxi and hold. Naming the measure removes the ambiguity, and lets a syndicate track an oil change on engine time while tracking its inspections on flying time.

Who can use it

Interval type is set when a maintenance item is created and cannot be changed afterwards. The measure a usage-based item counts against can be changed later by an admin, on the edit screen, provided the item is re-baselined onto the new measure in the same save (see Maintenance items). Both are visible to anyone who can view the item, but a member sees them read-only.

Where to find it

Create Maintenance Item screen: Interval Type dropdown (Hours, Day, Month or Year), and Counts against for hours items.
Edit Maintenance Item screen: Interval Type displayed as read-only text; Counts against as a dropdown for usage-based items for an admin, and as read-only text for a member. Changing it reveals a required Last Completed At field for the reading on the new measure, and, if the aircraft has no reading yet for that measure, a second required field for what it reads right now (see Maintenance items: Behaviour rules).
The chosen measure also appears wherever the item’s figures are shown, so a remaining-hours reading reads as “12.4 flying hrs” or “12.4 Tacho hrs” rather than a bare “12.4 hrs”.

Fields / options

Type	Family	Typical example	Available in create form
Hours	Usage-based	50-hour check, 100-hour check	Yes
Day	Calendar-based	7-day pre-flight check, 30-day check	Yes
Month	Calendar-based	4-month oil change, 6-month inspection	Yes
Year	Calendar-based	Annual inspection, ARC renewal	Yes
Cycles	Usage-based	Landing-gear inspections	No (see Behaviour rules)

Choosing between Day, Month and Year

Use whichever unit the aircraft’s schedule is actually written in. A check the maintenance organisation describes as “annual” should be a 1 year item, not a 365 day one: a year interval lands on the same date next year whatever leap days fall in between, whereas 365 days drifts a day earlier at every leap year and eventually stops matching the certificate.

Days remain the right choice for anything genuinely counted in days, such as a 7-day or 30-day check.

Measures an hours item can count against

The options offered are limited to what your syndicate actually records for that aircraft, set under usage capture. You cannot peg a check to something nobody writes down, because such a check would never come due.

The limit is enforced when the check is saved, not only in the picker. That matters if you were offline: your phone still shows the measures your syndicate recorded when it last synced, so if someone stopped recording one of them in the meantime, the check is refused when your phone reconnects and you are told why. Pick a measure the aircraft still records and save it again.

Option	What it counts	Offered when
Flying hours	Accumulated time in service — the finest span you record, wheels-up to wheels-down where you record it, otherwise brakes-off to brakes-on	You record flight or block times
Your meter’s own name, plus “hours” (e.g. “Tacho hours”, “Hobbs hours”)	The meter’s own face reading	You record the engine meter

A cycles item always counts landings and is not offered a choice.

Behaviour rules

Usage-based (Hours, Cycles). The item’s due-at value is a number on the scale of the measure it counts: last completed value plus the interval value. It becomes due when that measure reaches or exceeds the number. Because the measures are on unrelated scales — a meter face typically reads in the thousands while accumulated flying hours start from whatever the aircraft carried when it joined — a due-at value only means anything alongside the measure it belongs to.
A measure is required for usage-based items. An hours or cycles item cannot be saved without one. If your syndicate records only one usable measure, it is chosen for you.
The aircraft must already have a reading for the measure. An item counting something the aircraft has no figure for could never come due: there is nothing to compare it against, so it would sit in the list reading healthy for ever. A new aircraft is in exactly that state, because flying hours and landings are counted up from a starting figure nobody has given yet, and the engine meter only exists once somebody has entered its reading or flown the aircraft. So the create form, the template setup sheet and the edit form all ask what the measure reads on the aircraft now and will not save without it, and the database refuses the item too, so no other route in can skip it. The figure is recorded against the aircraft exactly as if it had been entered on the aircraft’s own edit screen.
Usage capture cannot be turned off underneath an item. An admin who unticks Capture engine meter on a syndicate or aircraft with items counting engine hours is stopped, shown which items are affected, and offered a link into the maintenance list to point each one at a measure the aircraft still records. Once nothing counts the engine meter, the capture change saves normally. Items counting flying hours or landings never block a capture change, because both are rebuilt from the usage logs whatever is captured. See Usage capture.
Calendar-based (Day, Month, Year). The item’s due date is computed by adding the interval to the last-completed date in the unit you chose. A 12-month item falls due 12 months later, and a 1-year item falls due on the same date the following year. Calendar items count no measure.
Month arithmetic clamps to the end of a short month. One month after 31 January is 28 February (29 February in a leap year), not 3 March. The item is never given a due date that does not exist, and never drifts a few days later each time it is completed.
A calendar interval has to be a whole number. Days, months and years are entered as whole counts — 18 months rather than 1.5 years. A fraction is refused when you save, on the create form, on the edit form, and by the database itself if a device tries to send one after being offline. There is no such date as “one and a half years after 10 March”, so a fraction would give an item a due date and a warning window that disagree by up to half its interval.
Cycles is not in the create form. Cycles items are counted correctly against landings and will ground the aircraft when past their limit, but cannot be created through the form. An existing cycles item is fully honoured.
Signing an item off offers to roll it forward. Completing an item records who completed it, when, and at what value; by default it also works out the next due point and offers it to you, pre-filled and editable, so you can accept it, change it, or decline. Declining leaves the item Completed, with nothing scheduled — the only outcome there used to be. A calendar item keeps its anniversary: the next due date is its previous due date plus the interval, so it falls due on the same date whichever day it was signed off on. A usage item counts from the reading at completion plus the interval. See Maintenance items: Behaviour rules.
A usage-based item may also carry a calendar limit, so a 50-hour check can also be “or 4 months, whichever comes first”. A calendar-based item cannot carry one, since it already has only the one clock. See Maintenance items: Secondary calendar limit.
Interval type is fixed after creation. The edit screen shows the type as a read-only label. To change it, remove the item and create a new one. The measure it counts against is editable.
Status calculation is identical across types. Percentage and absolute-threshold rules apply the same way, each against the item’s own measure. See Maintenance items: Behaviour rules.