VFR Obstacle Clearance Requirements

Once again, there are various exceptions when it comes to minimum altitudes and distances, based on the operating context.  Let's see if we can make some sense of it all.

Except for the purpose of take-off or landing....

CAR 704.23 (Commuter)

• Day: must be at least 500 AGL and 500 feet horizontal from any obstacle
• Night: must be at least 1000 feet above any obstacle within 3 miles of route

CAR 705.32:  (Airline)

• Day: must be at least 1000 AGL and 1000 feet horizontal from any obstacle
• Night: must be at least 1000 feet above any obstacle within 5 miles of route (2000 feet in mountainous regions)

How Far and How High?

There are so many different regulations that specify distances, heights, etc.  It's easy to get some of them mixed up.  So... time for a quiz to see which ones you know!  Questions here; answers and references in the links provided.

A low level airway is controlled airspace and extends from ________ AGL up to ___________. 
(Answer here)

A low level air-route is Class ___ airspace and extends from ____________ up to __________.
(Answer here)

A control zone normally has a _____ NM radius and the normal vertical extent is up to ______ AAE.
(Answer here)

When an aircraft is on a defense flight plan, the PIC shall revise the estimated time and point of entry/exit into the ADIZ if they vary by _____ minutes of _____ NM. 
(Answer here)

No person shall conduct a take-off in an aeroplane if the weight of the aeroplane is greater than the weight specified in the aircraft flight manual as allowing a net take-off flight path that clears all obstacles by at least ___ feet vertically or at least ___ feet horizontally within the aerodrome boundaries, and by at least ___ feet horizontally outside those boundaries.
(Answer here)

An airline operator may not operate an aeroplane at a weight which will not allow it to attain with any engine inoperative, a net flight path which has a positive slope at _____ feet above all terrain and obstructions within ___ NM on either side of the intended track. 
(Answer here)

The vertical dimensions of the Arctic Control Area (ACA) are FL____ and above.
The vertical dimensions of the Northern Control Area (NCA) are FL____ and above.
(Answer here)

The vertical dimensions of the Canadian Minimum Navigation Performance Specification Airspace (CMNPSA) within the Canadian Domestic Airspace (CDA) are FL___ to FL___.
(Answer here)

The vertical dimensions of RVSM airspace is FL___ to FL___ inclusive.
(Answer here)

The vertical dimensions of the North Atlantic Minimum Navigation Performance Specification Airspace (NAT MNPSA) are FL___ to FL___.
(Answer here)

Throughout the North Atlantic (NAT) Region, airspace at and above FL___ is Class __ airspace, while airspace below this level is Class __ airspace.
(Answer here)

An aircraft operating in the vicinity of an active forest fire should operate clear of the area by a minimum altitude of _____ AGL and a minimum distance of ___ NM.
(Answer here)

Altimeter Setting and Operating Procedures

Reference AIM RAC 2.11 and 2.12

ALTIMETER SETTING REGION

CAR 602.35 

• Departure: altimeter setting at aerodrome, or if not available the elevation of the aerodrome
• Enroute: altimeter setting of nearest station along route
• Arrival: altimeter setting at destination

STANDARD PRESSURE REGION

CAR 602.36

• Departure: altimeter setting at aerodrome, or if not available the elevation of the aerodrome
• Enroute: immediately prior to reaching the intended flight level, set 29.92
• Arrival: altimeter setting at destination
• Holding: once descending below lowest flight level of hold, altimeter setting at destination

TRANSITION BETWEEN REGIONS

CAR 602.37

• the simplest way to think about this is to always change the altimeter in the standard pressure region, whether it is a lateral or vertical transition

Room to Breathe

Mark Twain wrote, “The air up there in the clouds is very pure and fine, bracing and delicious. And why shouldn't it be?--it is the same the angels breathe.”

For all its beauty and truth, we also know that at FL250, our time of useful consciousness is a mere 3 to 6 minutes. Hence, there are regulations about oxygen... requirements for quantity, duration, training, etc.

GENERAL

CAR 605.31 Oxygen Equipment and Supply

• non-pressurized aircraft 
• if more than 30 minutes between 10 000 and 13 000 >> all crew and 10% of passengers (at least 1 passenger) 
• above 13 000 >> all persons (for at least 1 hour if air transport) 
• pressurized aircraft following emergency descent 
• similar, but a bit more complicated, see table in regulations 

CAR 605.32 Use of Oxygen

1. Where an aircraft is operated at cabin-pressure-altitudes above 10,000 feet ASL but not exceeding 13,000 feet ASL, each crew member shall wear an oxygen mask and use supplemental oxygen for any part of the flight at those altitudes that is more than 30 minutes in duration. 
2. Where an aircraft is operated at cabin-pressure-altitudes above 13,000 feet ASL, each person on board the aircraft shall wear an oxygen mask and use supplemental oxygen for the duration of the flight at those altitudes. 
3. The pilot at the flight controls of an aircraft shall use an oxygen mask if

• the aircraft is not equipped with quick-donning oxygen masks and is operated at or above FL250; or
• the aircraft is equipped with quick-donning oxygen masks and is operated above FL410.

FIRST AID OXYGEN

CAR 704.67 (Commuter): if flying above FL250 >> supply one passenger for one hour

CAR 705.72 (Airline): 2% of occupants (at least 1 person) for one hour


PORTABLE OXYGEN

CAR 705.94 (Airline): above FL250 >> 15 min supply for each FA

Do you know what might happen if you don't use oxygen when your body requires it?Everyone reacts to hypoxia differently.  I went to the FAA Civil Aero Medical Institute in Oklahoma City for some invaluable High Altitude Training.  

Section 24 of Standard 724.115 and Section 29 of Standard 725.124 both specify that 'High Altitude Training is required for all flight crew members operating aeroplanes above 13 000 ASL before first assignment on a pressurized aeroplane and every three years thereafter.'