In reality, with MSG-3, Block & Phased are practically the same thing, with the "phased" term being more standard—where tasks are added to standard A, B, C checks as the aircraft ages, or utilization (hrs/cyc) progresses, which are due with a specific threshold and repeating with an interval time.
(Since the advent of MSG-3, which was the game-changer and a true "block program," in higher-level checks have now pretty much disappeared.)

Essentially, packages are developed by selecting maintenance tasks into convenient checks that are appropriate for the type of operation and can range from short overnight checks to downtimes of a few days and everything in between.

It is a balance of operational availability, capacity planning of the facility, and the availability of manpower.

Scheduled maintenance tasks are grouped into work packages. The completed program may be referred to as a maintenance cycle.

A typical program would consist of a daily check (which can in fact be typically valid for up to 48 hrs). It is the lowest certifying maintenance scheduled check (Pre Departure Inspection - PDI is not a certifying check).

The accomplishment of the daily check requires little in the way of specific equipment, tools, or facilities.

As well as a walk-around inspection, a daily check includes Fluids / Fire worthiness / Emergency Equipment and general integrity of wheels and Brakes, possibly also specific lubrication.

At the next check level, typically called an "A check." A large number of tasks may be performed in a variety of packages (all showing compliance with the requirements of the Maintenance Planning Document (MPD).

This is a more detailed check of aircraft components and systems, it may be performed using additional test or service equipment. Typically does not any significant component disassembly or removal.

Checks are used as major fault-finding opportunities with General Visual Inspection zonal inspections being performed. In addition, many operational and functional checks will be carried out, as well as SB and Modification Programs (Mod) being carried out at this time.

Some short-haul operators equalize their "C check" tasks throughout every "A check" phase on overnight visits; often with a flight schedule to maintain the next day, thus never having extended ground time between Heavy Maintenance Visits (In the case of one operator, this is 6000 hours of operation).

In essence, there are two broad concepts: equalized vs. block checks.

Which one suits a given operation depends on a multitude of factors, including fleet size, operational set up, aircraft age, etc.

Sofema Аviation Services offers a range of Regulatory and Vocational training to comply with the requirements of EASA. Please see www.sassofia.com or our online training portal www.sofemaonline.com or email us at team@sassofia.com