Type Rating Knowledge — Cessna 172S NAV III

Cabin, safety and emergency equipment

The seats, restraints, doors and baggage areas — including the one-inch belt check that is a go/no-go decision — and then the three pieces of emergency equipment: the ELT, the Halon extinguisher that empties in eight seconds, and the CO detector that shares a subject with the cabin heating system.

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Seats, restraints, doors and baggage

Two kinds of seat

The front seats and the rear seat are not the same design, and the difference matters when you are briefing a passenger. The two crew seats adjust forward and aft with a handle below the centre of the frame, up and down with a large crank under the RIGHT corner, and their backs are INFINITELY adjustable using a release button in the centre front, just under the seat bottom. One behaviour worth knowing before it surprises you: on an UNOCCUPIED seat, the back folds forward automatically whenever that release button is pulled up. The rear is a single bench with a FIXED one-piece bottom and a THREE-POSITION reclining back, worked by a lever below the centre of its frame. Headrests are fitted front and rear and are adjusted simply by pushing them up or down.

FRONT INERTIA REEL — Overhead inertia reel for the front seats, on the CENTRELINE of the upper cabin. It locks up under sudden deceleration and is free the rest of the time.
REAR INERTIA REEL — Overhead inertia reel for the rear seats — OUTBOARD of each passenger, not on the centreline like the front pair.
SHOULDER PORTION — The shoulder half of the integrated assembly, paying out freely from the reel so the upper torso can move.
LAP RETRACTOR — Retractor assembly for the lap portion. No more than one additional inch of belt should come out once the lap belt is in place on the occupant.
LINK — The link you grasp with one hand and, in a single motion, extend and insert. Shoulder and lap are one assembly, not two belts.
BUCKLE — Buckle with a release button. Positive locking has occurred when a distinctive snap is heard — the sound is the check.
OCCUPANT — The restrained occupant — lap belt snug and low on the waist as worn normally in flight.
FRONT SEAT — Vertically adjusting crew seat: handle below the centre of the frame for fore and aft, a crank under the right corner for height, and an infinitely adjustable back with a release button in the centre front.
REAR BENCH SEAT — Fixed one-piece bottom with a THREE-POSITION reclining back on a lever below the centre of the frame — not the infinitely adjustable back of the front seats.
LEFT DOOR — Entry door with the KEY OPERATED LOCK — left door only. Inside handle has three positions: OPEN, CLOSE and LOCK, spring loaded to CLOSE.
RIGHT DOOR — Entry door at the front passenger position. No key lock — to lock the aeroplane you lock this one from inside, then close and key-lock the left.
OPENABLE WINDOW — Openable window in each cabin door, held closed by a detent latch on the lower edge. Either may be opened at any speed up to 163 KIAS. The rear side and rear windows are fixed.
BAGGAGE AREAS (2) — Two areas: behind the rear seat to the aft cabin bulkhead, and a further area AFT of that bulkhead. Reached through a lockable door on the left side or from inside the cabin.
BAGGAGE NET — Net with tiedown straps, secured to tiedown rings provided in the airplane.

Redrawn from POH 172SPHBUS §7, Seats / Integrated Seat Belt-Shoulder Harness (Figure 7-4) / Entrance Doors and Cabin Windows / Baggage Compartment — structure restated, not traced.

How do you adjust the height of a front seat?

With a large crank under the RIGHT corner of the seat. Right — a crank, not a lever, and always the right corner regardless of which seat you are in.

What can be adjusted on the rear passenger seat?

The back angle only, to one of three positions — the seat bottom is fixed and one piece. Right. There is no fore-and-aft and no height adjustment back there, which is worth saying to a passenger who is reaching for something that does not exist.

One assembly, and one measurement that decides the flight

Every seat position has an integrated seat belt and shoulder harness: an overhead inertia reel for the shoulder portion, a retractor for the lap portion, and one link that goes into one buckle. You grasp the link with one hand and, in a single motion, extend the assembly and insert it — and positive locking has occurred when you hear a distinctive SNAP. The reel positions differ front to rear: in the front seats the inertia reels are on the CENTRELINE of the upper cabin, and in the rear seats they are OUTBOARD of each passenger. Then comes the check that is not about comfort. With the lap belt in place on the occupant, no more than ONE additional inch of belt should be able to be pulled out of the retractor. If more comes out, the occupant is too small for the installed restraint system and the POH says the seat SHOULD NOT BE OCCUPIED until they are properly restrained. That is a go/no-go, and it is the kind of check that gets waved through precisely because it looks like a fit adjustment.

Where are the inertia reels?

Front seats: on the centreline of the upper cabin. Rear seats: outboard of each passenger. Right, and the asymmetry is deliberate — there is nothing on the centreline behind the front seats to hang a rear reel from.

A small passenger is strapped in and you can pull three more inches of lap belt out of the retractor. What does the POH require?

That seat should not be occupied until the occupant is properly restrained — the restraint system does not fit them. Right, and it is stated as a condition on occupying the seat, not as advice. More than one additional inch is the threshold.

Doors, windows and the one that opens in flight

There are two entry doors, at the front seat positions. Both have a recessed exterior handle, a conventional interior handle, and a door stop mechanism — but only the LEFT door has a key operated lock. That is what fixes the locking sequence: lock the right cabin door with its inside handle, close the left cabin door, and lock it with the ignition key. Inside, the handle has three positions placarded OPEN, CLOSE and LOCK, and it is spring loaded to CLOSE. Both doors carry openable windows, held shut by a detent latch on the lower edge of the frame and helped open by a spring-loaded retaining arm; either may be opened at ANY speed up to 163 KIAS. The rear side windows and the rear windows are fixed. And the door that opens in flight has its own note: it does not constitute a need to land. Set up trimmed at approximately 75 KIAS, momentarily shove the door outward slightly, and forcefully close and lock it.

Up to what speed may a cabin door window be opened?

163 KIAS — either window, at any speed up to that. Right, and it is the same figure as the aeroplane’s Vne in KIAS, which makes it easy to remember and easy to misattribute.

Which door has the key operated lock?

The left door only — so the right is locked from inside, then the left is closed and key-locked last. Right, and that single asymmetry is what dictates the whole locking sequence.

Cabin (POH 172SPHBUS §7 — Seats, Restraints, Doors and Windows, Baggage Compartment)
Item	Detail
Front seats	Fore/aft handle below the centre; height crank under the RIGHT corner; infinitely adjustable back
Rear seat	Fixed one-piece bottom; three-position reclining back on a lever below the centre
Front inertia reels	Centreline of the upper cabin
Rear inertia reels	Outboard of each rear passenger
Lap belt check	No more than ONE additional inch out of the retractor with the belt in place
Key operated door lock	Left door only
Inside door handle	Three positions: OPEN, CLOSE, LOCK — spring loaded to CLOSE
Openable windows	Both cabin doors, any speed up to 163 KIAS; rear windows fixed
Door open in flight	Not a reason to land — trim at approximately 75 KIAS, shove out slightly, close and lock forcefully
Baggage	TWO areas, forward and aft of the aft cabin bulkhead; lockable door on the LEFT side; net with tiedown straps

How many baggage areas are there, and how do you reach them?

Two — one behind the rear seat to the aft cabin bulkhead and one aft of that bulkhead — reached through a lockable door on the LEFT side or from inside the cabin. Right. The second area behind the bulkhead is the one people forget exists, and it is further aft, which matters for the weight and balance.

ELT, fire extinguisher and CO detection

The ELT, and what ARM actually means

The emergency locator transmitter fitted to this aeroplane is an Artex ME406: a solid-state two-frequency transmitter powered by its OWN internal lithium battery, in the tailcone along the right side behind the baggage compartment aft panel, with an external antenna on top of the tailcone. Its own battery is the important architectural fact — nothing about the aeroplane’s electrical system matters to it. You control it from a two-position rocker on the upper right instrument panel. ARM is the normal position, and it means off-but-armed: the transmitter is energised only when the internal "G" switch senses longitudinal inertia forces to TSO-C91a/TSO-C126. ON energises the transmitter immediately, BYPASSING the automatic activation switch. There is also an ARM/ON switch and a warning light on the transmitter unit itself, back in the tailcone.

G SWITCH — Internal inertia switch. With the remote switch at ARM the transmitter fires only when this senses longitudinal inertia forces per TSO-C91a/TSO-C126.
ELT REMOTE SWITCH — Two-position rocker on the upper right instrument panel: ARM (off, armed) and ON. ON bypasses the automatic activation switch and transmits immediately.
CO DETECTOR — A single detector behind the instrument panel, powered by the airplane’s DC electrical system and integrated into the G1000.
ARTEX ME406 — Solid-state two-frequency transmitter powered by its OWN internal lithium battery, in the tailcone along the right side behind the baggage compartment aft panel. It carries its own ARM/ON switch and warning light.
G1000 — The CO system is integrated into the G1000 rather than being a standalone detector with its own display.
ELT ANTENNA — External antenna mounted on TOP of the tailcone.
RED WARNING LIGHT — Flashing red light directly above the remote switch. It is the visual half of the pair — there is also an unusual aural warning, easily heard by the pilot.
CO LVL HIGH — Flashing warning annunciation in the PFD annunciation window at 50 PPM or greater, with a continuous tone until the softkey below WARNING is pushed. It then stays steady until the level drops below 50 PPM and resets itself.
121.5 MHz — Standard swept tone on the international VHF frequency, transmitted until battery power is gone. It is what SAR homes on to pinpoint the beacon.
406.028 MHz — A 440 millisecond burst every 50 seconds, for the FIRST 24 HOURS only, carrying programmed identification data to the COSPAS/SARSAT satellites.
HALON 1211 — Portable Halon 1211 extinguisher on the floorboard between the front seats, classified 5B:C. Entirely manual — drawn unconnected because it has no electrical connection of any kind.

Redrawn from POH 172SPHBUS §7, Cabin Features (Cabin Fire Extinguisher, Carbon Monoxide Detection System) and §9 Supplement 1, Artex ME406 ELT — structure restated, not traced.

What does the ARM position on the ELT remote switch do?

Turns the transmitter off and arms it, so it activates only if the internal "G" switch senses the required inertia forces. Right — it is a conditional off. ON is the position that bypasses the G switch and transmits immediately.

How do you know from the cockpit that the ELT is transmitting?

Two ways: an unusual aural sound that is easily heard, and a flashing RED light directly above the remote switch. Right — aural and visual, deliberately, so an inadvertent activation on the ground is noticed rather than left running.

Two signals doing two different jobs

When the ME406 is energised it transmits the standard swept tone on the international VHF frequency of 121.5 MHz, and it keeps doing so until battery power is gone. That signal is monitored by general aviation, commercial aircraft and government agencies, and its job is to let searchers PINPOINT the beacon once they are looking. In addition, for the FIRST 24 HOURS ONLY, it transmits a 406.028 MHz signal at 50 second intervals — each burst 440 milliseconds long, carrying identification data programmed into the ELT and received by COSPAS/SARSAT satellites. That data may include the aircraft ID, the ELT serial number, the country code and the COSPAS/SARSAT ID. So the two signals are not redundant. The satellite burst says WHO and roughly where, quickly, for a day. The 121.5 tone says exactly where, for as long as the battery lasts. And the identification is only meaningful if the ELT has been REGISTERED with the applicable civil aviation authority — which the POH makes the owner or operator’s job before use.

What is the 406.028 MHz transmission, and how long does it last?

A 440 millisecond burst every 50 seconds carrying programmed identification data to COSPAS/SARSAT satellites, for the first 24 hours only. Right on all three. After 24 hours the satellite signal stops and 121.5 MHz continues alone until the battery dies.

A forced landing is coming, in mountainous terrain. What does the ELT supplement tell you to do?

Set the remote switch to ON BEFORE landing — do not rely on the G switch to activate it. Right, and the supplement says it is very important in remote or mountainous terrain. ON bypasses the automatic switch entirely.

Eight seconds of Halon

A portable Halon 1211 extinguisher sits in a holder on the floorboard between the front seats, classified 5B:C. Check it before every flight: the gauge at the top within the green arc — approximately 125 psi — and the operating lever lock pin securely in place. To use it, loosen the retaining clamps and remove it from the bracket, hold it upright, pull the operating ring pin and press the lever, directing the liquid at the BASE of the fire at the NEAR edge and progressing toward the back with a rapid side-to-side sweep. Two facts turn that from a procedure into a plan. The contents empty in approximately EIGHT SECONDS of continuous use, so there is no second attempt and no time to aim badly. And there is a WARNING attached: ventilate the cabin promptly after successfully extinguishing the fire, to reduce the gases produced by thermal decomposition — Halon on a hot fire produces things you do not want to breathe. Afterwards it must be recharged by a qualified fire extinguisher agency before it goes back in its bracket.

How long will the cabin fire extinguisher last?

Approximately eight seconds of continuous use. Right — which is why aiming at the base of the fire at the near edge, rather than at the flames, is the difference between putting it out and emptying the bottle.

The fire is out. What does the POH warn you to do next?

Ventilate the cabin promptly, to reduce the gases produced by thermal decomposition of the extinguishing agent. Right, and it is printed as a WARNING. Halon on a hot fire decomposes into products you should not be breathing in a closed cabin.

How do you establish which ELT is fitted to the aeroplane you are about to fly?

From its equipment list and the supplement in its own POH — two installations are approved, and the serial block does not decide it. Right. Supplement 1 is the ME406, Supplement 2 the C406-N, and the aeroplane’s own paperwork is what says which applies.