"Starter engaged" warning light
 

Another thread presented a sideline discussion on "starter engaged" warning lights. I did not realize that they were a requirement on UK aircraft - what a great idea! But, what do the supplements say about an illuminated light?

I would guess that the light indicates that the solenoid (contactor) which controls the starter motor, is energized, and presumably, that the motor is turning. Obviously, when this is unintended, it is bad, and is good cause for stopping the engine as soon as safely possible. Certainly these solenoids do stick engaged, and otherwise fail, so an indicator of their status is great, as long as the pilot knows what they are being told - The motor is energized.

However, every starter system includes a clutch or drive release of some kind, to engage, and disengage, the starter drive from the crankshaft. These mechanizms, in their various forms are every bit as troublesome as the solenoid, and their failure (usually a seizure) creates an even more unsafe situation.

When the stater motor, with an otherwise functional "clutch" does not stop running, because the solenoid has remained engaged, it is very likely that a Lycoming, or small continental engine will simply "over run" the starter drive, and operate more or less normally. Yes, the starter motor itself, is going to get really hot, and is certainly a fire and self destruction hazard, but otherwise, is not affecting the operation of the engine itself. The large Continental is a different matter.

A starter solenoid and motor can operate properly, and you can still have a starter problem, which is more serious, and costly.

In a Lycoming, a sticking "Bendix" happens from time to time. This means that the pinion which engages the ring gear, did not withdraw after the starter was de-energized. A careful pilot ear can sometimes hear the ringing howling sound of spinning Bendix. No warning light, but good cause to shut the engine down right away.

In Continentals, gears do not engage and disengage. The smaller Continentals, have an over running clutch, which are known to seize. When this happens, the starter motor is accelerated to a rotational speed far in excess of the design, and it's probably going to fly apart, and seize. This is going to cause something in the engine drive line to break. The larger Continentals employ a worm drive and clutch spring. These are known to seize and overheat. There are a number of reasons for, and variations on this failure, which are too much to describe here. In short, a running on motor in these engines is bad for several reasons, and there are other failures, which do not involve an energized motor.

So, just because your "starter engaged" warning light is not illuminated (it probably should be called a "starter energized" warning light), there could still be a failure of the starter system, which is every bit as serious. Be "at one" with how your engine should sound and operate just after start. If it is not right, shut it down, and have the maintainer have a look..

The POHs for the types I have flown mention possible (likely) damage to the electrical system if the starter continues to operate when the engine is running, so I always thought that was the main risk (apart from damage to the motor itself).

Smithy

A random input and slightly off pitch perhaps on the name of said light indicator. I tend to use the Pooleys wire-bound checklists (take them however you will :oh:); for both Cessna and Piper types it calls it the 'Starter Warning Light'. Interesting to hear if there are any odd variations on this?

That's essentially what it is!

First check after releasing the starter key is to check this light extinguishes - if not then shut down and call the engineer!

I had a student once manage to start a C150 with the key in upside down. It started but the starter switch stuck in the start position. The only obvious indication to me was the starter warning light. I suspect, if it was my hand on the key switch, I would have noticed something amiss that a low hour student may not.

The requirement was in CAP747 (GR no. 1) but I now think it is an EASA requirement.

It is relatively easy to take a wire from the output of the starter solenoid to light the warning light when there is 14V at the starter.

If the starter is still engaged (Bendix stuck in) but the switch is released, does the light stay on?

Wired as described just above, it should. The key word being "output of the solenoid".

Not necessarily. If power is still being applied because of a faulty switch or solenoid, then the light will illuminate.

However, if it is a jammed pinion then the light will not be illuminated, but the starter will be engaged and the engine will be spinning it. As the gear ratio is about 10:1 it will spin the starter at 10x the engine revs so can do a lot of damage. I have had one jam, and because the engine is driving the starter so fast I think heat is generated so the pinion jams further. The mechanic was unable to release it, even after removal from the aircraft. We had to fit a new starter.

Shirley the solenoid is just an electromagnetic switch that requires an input before it can "output"/move? If the solenoid is stuck on then power will remain to the starter motor direct from the battery? I don't think the solenoid has an "output" as such, it just opens a heavy switch to connect the battery/starter motor.

Zulu Alpha. that's the way I read it.

I should have said that it was only discovered when I pulled the prop through before starting.
It must have jammed on the previous start but there was no indication in the cockpit during a 30 min flight. No light on and no difference to the engine note.

You could clearly hear it on pulling the prop through though.

Mandatort Starter Engaged Light in the UK and ?? EU
 

Is there anyone out there who can tell me where / when / how the CAA & EASA wrote the legislation to mandate the installation of a "starter engaged" light?
Was the equivalent to an STC required or did the CAA / EASA merely provide an acceptable" wiring diagram?

Pilot DAR, you made me think about this, always assumed it was more sophisticated than just a light on the starter side of the solenoid, but perhaps it isnt. I always thought it worked on back emf from the starter acting as a generator because the likely mode of failure is failure of the bendix to retract but actully its just as likely that the solenoid could stick. I would say that it probaby does work to indicate both modes of failure actually and is thus ingeneous in its simplicity,

I've started a 152 with my home garage key. I reckon a bent nail would do just as well.

GR no.1 was removed in Sept. 2005. I believe the UK was the only place to have that requirement and there was little enthusiasm to make it a European requirement. I believe it originally came about following a single incident of an accident attributed to a 'stuck starter'.

Those that I have seen typically just take a wire from the output side of the starter solenoid directly to the cockpit annunciator.

My Archer II (US reg and based in the Caribbean) does not have such a light - sounds like a good idea though; I can see that the starter may continue to draw battery power and drain it to the point where comms and nav kit goes inop - a big issue here as 99% of time is spent over water.

Was it an STC mod? Any one know of a PA28 kit of parts or a tech spec for the light?

When I renewed the C of A for my old Beagle Terrier back in 1995-ish, it was inspected by a CAA surveyor. He picked up that it had never had the 'starter warning light' fitted!

At that time Aircraft Spruce sold a little warning light and sensor which you simply added to the busbar. It sensed busbar voltage and so with a starting load it would come on. Equally it doubled as a 'low volts' warning.

Although uncertified our surveyor was happy with it. shame he did not look at the quality of the other work - the exhaust literally fell off and head gasket failed within 5 hours!

A shocking generalisation, but in cars, tractors, etc there are two types of starter drive: Those that rely on the motor rotation to throw the drive pinion into the starter ring and those that use the starter solenoid to physically move the pinion into engagement. The latter 'pre-engaged' starter solenoid only closes the motor contacts when the pinion has moved far enough to engage the ring gear. Both types have the 'Bendix' gear (a spring loaded reverse spiral) to throw the pinion out of engagement when the engine starts.

Pre-engaged starters can easily stick in the engaged position and in that event only the Bendix prevents over-running. The motor continues to receive power even when the key is released and major damage is inevitable because it's not continuously rated. I've always assumed the typical Lycoming starter is of this type and that the warning light indicates the position of the solenoid lever that pushes the pinion into engagement.

Could someone who knows better than I confirm please?

Bendix drives can also stick , but I doubt that any pilot would fail to notice this condition for long due to the noise, burning smell, engine disintegration etc. Engaged starters and sticking Bendixes continue in contact with the ring gear and this accounts for the worn away starter rings often seen in classic cars. Owners of these vehicles must be semi-deaf, if not before, then afterwards.

Preengaged types dont have bendix, the solenoid return spring pulls the pinion out. Aren't original lycoming starters generally bendix types but people like sky tec supply preengaged as superior aftermark replacements becauuse bendix is a cheaper, arguably lighter but technically inferior method , indeed prone to jamming in the engaged position. Pretty sure the original reason for the starter warning was stuck bendix, but Im sure someone who actually knows the detail will chip in shortly...

From the aopa training website, sums it up pretty well..

Although Bendix drives were phased out of the automotive world in the mid-1950s, they are still standard equipment on some new airplane starters. However, the B&C Specialty Products starter uses a linear actuator, and the Sky-Tec starter uses an electromechanical actuator to replace the Bendix drive. If the engine doesn't start, the Bendix stays extended, meshing tooth-to-tooth with the ring gear. An extended Bendix can create problems if hand-propping is required.

@ Victorian...I think you are mistaken!
A normal P/E starter- pinion has straght splines along which it slides to engage/disengage. The pinion has a one-way clutch (see my contributions to the "engine-starting" thread, for a full explanation.
the pinion stays in engagement whilstthe solenoid is energised. As the starter is geared at around 30:1 (pinion is about 4cm diam. witharound 8 teeth ring-gear around 50 cm dia . Typically a starter will crank an engine at about 80rpm and when the engine starts, it will tick-over at around 600-850 rpm. If the starter is continually engaged, the overrun-clutch will still transmit power...from the engine to the starter.....starter is not built to do10,000 rpm plus.....they literally throw their windings from the armature by a combination of centrifuging and the com-solder melting...welded coms have disintegrated!the segments flying off ,still attached to the winding-tailsand destroying the brush-gear and anytinig else in range.
A stuck solenoid is not that common, a more likely suspect being the key-switch or a relay with the contacts "arc-welded" together....also can happen with a low/duff battery (volts low, current high.)

the reason old cars wear the ring-gear is due tio the engine always stopping with one cylinder coming on compression....on a four-cylinder car, you'll see a worn ring-gear has four distinct wear-slopes around it's periphery the most heavily worn is where the engine always stops, so every start , the pinion smacks into those same teethand grinds away to pull that cylinder over compression....then the load eases until the next one ....that's why the wear is progressive....split a ring and straighten it out and it 's wear-pattern is four ramps...eventually, the teeth become that worn that the pinion doesn't travel far enough to engage...a new pinion can be a stopgap fix!

P/E engagement forks are invariably connected to the solenoid-plunger via spring-loading, so even if the pinion doesn't mesh, but hits a tooth on the ring, the plunger will still move against the springs and close the solenoid main contacts.....as soon as the starter motor turns, the pinion will go into mesh...again, it's very rare to get a jam.