Yes, combustion cabin heaters can be very safe to operate when properly maintained. Pilots and owners need to take an active role in making sure these heaters receive the service they require to remain safe and reliable.
What do you know about your airplane's heater? Here is a minimum list of things you should know:
• The heater's manufacturer;
• Any ADs associated with the heater;
• How to comply with the ADs
(and the risks if you don't); and
• Your options for compliance.
It is important you know your heater's manufacturer, if nothing else, because each manufacturer has a different maintenance manual and that document is vital to proper servicing of the heater. Manufacturers of combustion heaters include Janitrol, South Wind and C&D Associates.
The first place to look for your heater's manufacturer is the name on the data plate. If you can't read the data plate, look at the terminal strip—an electrical connector that sits on the body of the heater—Janitrol is numbered 1-6 or 6-1, while South Wind is numbered 4-10 or 10-4. (The third company, C&D Associates, is a manufacturer of direct replacements through PMA, but the terminal strip will reflect the original manufacturer's numbering.)
Once you have determined the heater's manufacturer, you'll be able to look for ADs. There are currently three ADs directly affecting combustion heaters.
The Big Three
AD 2004-21-05 pertains to Janitrol's B series heaters and requires mandatory inspections at 100 heater hours or 24 calendar months, whichever occurs first. The two areas of concern that prompted this AD are the combustion tube (burner chamber) and the combustion air pressure switch. The combustion tube has been known to weaken or leak over time, and this could result in a fire or explosion according to the AD.
Janitrol developed the procedure we know of as the pressure decay test (PDT), and you can now perform a PDT without removing the heater from the aircraft with test equipment designed by Dennis Sandmann, the founder of C&D Associates, Inc.
FAA approved the pressure decay test which requires all openings to be sealed and air pressure of 6 psi to be applied and indicated on the gauge. If the pressure drops below 1 psi after 45 seconds, it indicates a significant enough leak that the tube is considered to have failed the PDT. A failure means the combustion heater would need to be overhauled or replaced.
AD 2004-21-05 also requires testing of the air switch to make sure it turns on and off at the proper airflow pressures. To test this switch, you must refer to the Maintenance Manual 24E25-1 Rev D.
After testing both of these areas, the heater would need to pass a functionality test and could be returned to service.
AD 2004-25-16 (Revision 1 adopted June 20, 2005), addresses the fuel regulator shutoff valve. The concern for this valve is that it may leak fuel; the AD requires a mandatory inspection for leaks every 100 hours or 12 calendar months.
If a leak is found, the AD requires replacement with a valve that has a date code of 02/02 or newer.
All South Wind/Stewart Warner/Meggitt heaters (8240 through 8472 series) are subject to AD 81-09-09. This AD requires mandatory 250-hour inspections and 1,000-hour overhauls.
One of the critical differences between this AD and the other two is that there is no calendar time (i.e., "X number of months/years") attached to the AD.
This AD requires a visual inspection of the ventilating and combustion air inlets, exhaust, fuel lines, drains and electrical wiring at 250 hours. The inspection is followed by an operational inspection (also required at 250 hours).
When the heater reaches 1,000 hours, the unit and its accessories must be overhauled. Proper overhaul includes a PDT; if the combustion tube passes the PDT, it does not need to be replaced. However, C&D Associates reports it has never seen an original tube make it past 1,200 hours.
No PDT is required between overhauls, but this is one change being proposed in a Notice of Proposed Rulemaking (NPRM) for an AD scheduled to supersede AD 81-09-09.
According to the document issued by FAA on Aug. 20, 2014, "Within the next 10 hours TIS or two calendar months after the effective date of this AD, whichever occurs first, and repetitively thereafter at intervals not to exceed 250 hours of combustion heater operation or two years, whichever occurs first, do the PDT...".
The FAA estimates "this proposed AD affects 6,000 combustion heaters installed on, but not limited to, Piper Aircraft, Inc. and Cessna Aircraft Company."
Comments on this NPRM closed on Oct. 6, 2014. (See Resources for a link to the NPRM as well as an article by Dennis Sandmann discussing the AD and its ramifications. —Ed.)
C&D's AMOC and recommendations
C&D offers Alternate Method of Compliance (AMOC) for all three of these ADs. Further, South Wind heaters overhauled by C&D Associates—that is, those with yellow data plates—are excluded from the current AD 81-09-09 as well as the upcoming AD.
C&D Associates does not have an AD applied to its PMA TSO-C20 heaters. These TSO-C20 heater replacements have been manufactured by the company since 2000 and are available for most all twin engine aircraft, from a Beech Baron to a Cessna 401/Piper Seminole. More details can be found on the C&D website.
C&D Associates requires a PDT at 1,000 heater hours and every 250 heater hours or four years, whichever comes first. The company recommends every new C&D heater to be overhauled at 2,000 hours or 10 years, and recommends annual calibration of pressure decay testers.
If your cabin heater is subject to an AD, you must comply. Your safety and the safety of your passengers could be at risk if you operate a heater that is out of compliance and/or not regularly inspected. (See the sidebar on page 31 for more information. —Ed.) If your heater does not comply with an AD, you must disconnect the heater so it cannot be turned on inside the cabin.
Instead of disabling your cabin heat, you do have an option that can relieve you from a demanding heater AD. C&D Associates offers pilots and owners AMOC solutions for heater ADs, whether it's an overhauled unit or a PMA direct placement.
TSO-C20 PMA direct
C&D Associates, Inc.
AD 2004-25-16 R1
NPRM to supersede AD 81-09-09
from C&D Associates
"South Wind Aircraft
"New South Wind Heater AD"