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Mobile Crane Operator (339A) Red Seal Exam in Ontario

Certifying authority: Skilled Trades Ontario (STO). Last checked 2026-09-10.

Certification is required in Ontario

This trade is on Ontario’s compulsory list as Hoisting Engineer — Mobile Crane Operator 1 (339A) / 2 (339C). Under Skilled Trades Ontario, workers must hold a valid Certificate of Qualification, a Provisional Certificate of Qualification, or a Registered Training Agreement; journeypersons must renew their C of Q each year. Official list PDF is dated Feb 2022; the count of 23 still matches the current STO page.

Source: Skilled Trades Ontario — Compulsory Trades (23 trades)

Preparing for the Mobile Crane Operator (339A) exam in Ontario?

Start with 10 free interactive Mobile Crane Operator (339A) questions with worked explanations, or take a full 110-question timed mock exam weighted to the official RSOS breakdown.

Try the 10-Question Interactive Mobile Crane Operator (339A) Quiz & Free PDF → Take Full 110-Question Timed Mock Exam ($14.99 CAD) →

Or unlock all Mobile Crane Operator (339A) questions with the 7-Day Pass ($9.99) or 3-Month Pass ($69.99, Free-Until-You-Pass Guarantee).

Whether it is required or not, the exam itself is the same paper everywhere in Canada. What your province decides is whether you must hold the certificate, how you apply, and where you sit it.

The exam: 110 questions, 7 Major Work Activities

The Red Seal Occupational Standard sets the split below. It does not change by province.

Major Work ActivityWeightingQuestions
MWA A: Performs common occupational skills 6% 7 Qs
MWA B: Performs hoisting calculations 18% 20 Qs
MWA C: Inspects and maintains crane 13% 14 Qs
MWA D: Performs rigging 12% 13 Qs
MWA E: Plans lift, prepares site and sets up crane 15% 16 Qs
MWA F: Assembles, disassembles and transports crane 14% 15 Qs
MWA G: Operates crane 23% 25 Qs

Source: Red Seal Exam Breakdown — Mobile Crane Operator (339A), red-seal.ca

Time allowed and pass mark

4 hours, and a 70% pass mark (77/110). These are set provincially rather than by the Red Seal standard, and the four hours is the same whether your paper is 100 or 150 questions.

Confirmed against Skilled Trades Ontario’s Exam Preparation Guide and SkilledTradesBC. Check your own authority before exam day.

Quick 3-Question Mobile Crane Operator (339A) Readiness Check

Click any option (A–D) below to grade yourself immediately and view the worked explanation:

Sample Question 1 of 3
A 100-tonne hydraulic truck crane is setting up on a compacted granular fill pad beside a new warehouse in Mississauga to erect roof trusses. The pad looks firm, but the lift plan shows outrigger loads of over 40 tonnes at the worst swing position, and the crane arrived with only its bare steel floats. What must be done before the outriggers are set down?
A) Set the bare floats on the gravel, since compacted fill can carry any outrigger load
B) Place mats or pads sized to keep ground pressure below the soil's bearing capacity
C) Set the outriggers at mid extension, so that less load is pushed into each float
D) Leave the tires in contact with the ground, so they take part of the crane's weight
Correct answer: B

Outrigger loads on a bare float can far exceed what compacted fill will carry. Mats or pads of adequate area spread the load so the ground pressure stays below the allowable bearing capacity. Tires must be clear of the ground when the crane is on outriggers. Compacted fill has a limit, and setting the outriggers at mid extension lowers the chart capacity instead of making the float load safe.

Sample Question 2 of 3
After a full overnight slow charge on a 12-volt flooded crane battery in Kingston, the mechanic tests each cell with a hydrometer. Five cells read 1.280 specific gravity, but cell 4 reads only 1.150. The battery has been slow to crank the engine for a week. What does this result show?
A) Cell 4 has failed, so the battery needs to be replaced
B) The electrolyte has evaporated, so acid must be added
C) The battery is healthy and only needs a short boost
D) The cells will even out after a long drive on the road
Correct answer: A

Healthy cells read within about 0.050 of each other. A cell 0.130 lower than the rest after a full charge is shorted or dead and cannot be recovered, so the battery is replaced. Adding acid is not the fix, a healthy battery has no such gap, and a drive does not revive a dead cell.

Sample Question 3 of 3
The outrigger box of a telescopic crane is positioned on the frame in Brandon, and the fittings have been wiped clean. The bolts and the hose couplers are laid out, and the manual has a tightening value. The crew's lead hand has gone for lunch. What is the right way to finish the job?
A) Connect the hoses and test the jack, and tighten the fasteners once the crane has gone to work
B) Fit two of the fasteners for now, since the rest of them are only needed for highway travel
C) Fit the fasteners to the manual's value, then connect the hoses and wiring and test the jack
D) Tighten them as hard as possible with an impact gun, because a tighter bolt is a stronger bolt
Correct answer: C

Fasteners are fitted to the manual's value, then hoses and wiring are connected and the jack is tested. Testing before fastening can twist the box, all the fasteners carry working loads, and over-tightening can stretch or break a bolt.

Where you write it in Ontario

Booking is handled by Skilled Trades Ontario (STO); confirm current locations and dates with them.

Preparing for the Mobile Crane Operator (339A) exam

Our Mobile Crane Operator (339A) question bank is built to the official RSOS weighting above, with a worked explanation and code citation on every question.

Continue to Full 10-Question Interactive Mobile Crane Operator (339A) Quiz → Take the full 110-question timed mock exam →

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