This is probably a basic question but our club just got a PA28-180 added. The manual calls for the start to be on the left magento very specifically. The other planes I have flown have both been 172s (a 1964 172D and a 1976 172M); this Cherokee is 1963 but in my limited experience I have not encountered the start on a specific magneto and wondering if someone could explain why. I have no issue with the procedure just curious and trying to understand the reasoning. Thanks in advance.
I'm no A&P but (usually, but not always) the left mag is the one with the impulse coupling and (usually, but not always) the keyswitch will ground the right mag when you turn it to the start position. IIRC the impulse coupling changes the timing when it's doing its thing, so if you had it on both, the mags would be timed differently, leading to a suboptimal starting experience.
The left magneto is usually the mag with the impulse coupling, which delays and intensifies the spark during startup. On most airplanes, the ignition key grounds out the right mag, so only the left mag provides spark (impulse). The timing of the spark from the left mag is delayed during engine start, so it will start easier. Once the key is released from the start position, the timing of the spark goes back to normal and the right mag starts to fire.
Thanks for the quick responses...that makes sense. Again, the POH was good enough for me but when I asked the person checking me out in the plane about it they said I'd need to find someone with a deeper knowledge of the specifics on that system as the Cherokee 180 they previously owned was newer and did not require starting on left magneto (maybe a key start where the key grounds the other magneto).
what a disgrace Seriously, if you're going to instruct in a plane, never mind check someone out in it you should know that plane well. One thing to not know specific torque value of individual airframe bolts, but the reasoning behind why procedures are the way they are should be evident
To be clear when I say "check out" that process is to clear me to fly the club plane so forgive me if I used the wrong term. My first google search found for check out from a rental company demonstration of 3 take-offs and landings, simulated engine out, stalls and basic flight maneuvers, and show you are a safe and competent pilot. That's the nature of the check out I'm talking about and while I'd agree deeper knowledge is ideal (it's the reason I asked my question) I'd disagree in that setting that what I described qualifies as a "disgrace".
@groomsie if we're going to be safe pilots there ought to be more to a checkout for proficiency than simply the bare minimum 3 TO/LDF, engine out, stalls, steep turn, etc. Yes - I know this is most club's definitions of check outs and satisfies the bare minimum (as a renter I know this as well). But, as competent proficient pilots who will be able to safely handle situations that are belly up it's important to understand at least the most basic aircraft systems. The powerplant and its magnetos, and how critical it is to safe flight, being one of them. Good on you for asking. The person doing the checkout should have known. Not to be totally pedantic, but hell it's POA, it's in the PPL ACS 14 CFR 61.105 as well, "Aerodynamics, Powerplants, and Aircraft Systems".. One thing to know things by rote "checklist says start on left" but real knowledge is in understanding the systems, beyond rote memorization. A common grief I have with CFIs is their general poor understanding of powerplant operation, proper leaning technique, etc. It's arguably the single most important part of the plane. Like I said, good on you to ask, happy flying and no harm intended!
All the Cherokees manufactured prior to the late 1960s had a separate push button starter switch and had owners manuals that included the recommendation to start on the left magneto only. The later airplanes that used the key switch to run the starter incorporated the grounding of the right magneto in the start position into the switch.
How is knowing why you start on the left mag critical to safe flight?????? A check out is NOT a Check Ride or even a Flight Review.
Knowing why you do something often prevents or mitigates future failure. Without knowing why you do something and just being told to do it frequently leads to not doing what you were told to do. For instance if you didnt know the impulse coupler retards timing during start up, one might assume starting on both might be better, not realizing it could cause kickback. I also have a 63. Key to left mag, push button start.
If you have an EIS on the right and an IC mag on the left, then starting on both actually is better. But other than that, I wholeheartedly agree with you in that knowing is one thing but understanding is different and better. For example, if the EIS is on the left and a non-IC mag on the right then you'll need to start on the left to avoid kickback.
Kudos to the OP for actually reading the POH. Seems to be a rare thing, and I note that many airplanes are lacking an Owner's Manual or POH or AFM altogether even though the law requires it to be in the airplane and accessible. So many questions show up here that are addressed in the manuals. And his question as to why is also legitimate. I always appreciated students that wanted to know why procedures in some airplanes were different than in others.
The point is, this is a nice thing to know why, or you can follow the checklist. And I applaud the OP for reading the POH and asking. But this is NOT a critical to flight issue. Yes, not knowing and not doing it can cause issues. But it is not going to cause you to crash. I remember a friend was doing his 757/767 type rating. One type rating for both. One student was trying to figure out how to remember which way the main gear retracted (one retracts forward, one aft). My friend looked at him and said, it is easy, you put the handle up, the gear goes up, you put the handle down, it goes down.
Spin the engine backward often enough, it'll become a flight safety issue. I know guys that would start on both mags thinking they get twice the spark. When I explain why the response is usually "oh, that's why it's kicked back before".
