We just purchased a 1977 Beech Sierra, and we have already had a few burned-out landing light bulbs and taxi light bulbs (located in the same compartment). I would like to find out from the group whether this is a frequent occurrence for many of you, what you did to fix it, and if there preventive maintenance/operation that can be done to minimize the frequency. Any feedback would be appreciated.
(Search strings: landing lights, taxi lights, light bulbs, lamps, HID, burned out, bulb replacement)
I’ll preface my comments with these observations:
I have never had a #4313 250W landing light burn out, since I installed a new one after buying the plane in early August of 1988. I have put more than 2,000 hours on the plane since then. I have not flown much at night in the past two years, but frequently flew at night before then. I only use the high-wattage landing light for actual landing.
I have taxi lights in both wings, both of which I installed myself using original Beech parts (as they were a factory Beech option).
I have a Precise Flight Pulse Light System, that can alternately flash the taxi lights. I use this system whenever it is hazy (most of the time in Florida); whenever we are approaching a towered or non-towered field; whenever we are flying an IFR approach that has a ceiling above pattern altitude (meaning possible VFR pattern traffic); and whenever we are called out as traffic to another plane, or when we receive a traffic call.
We almost certainly have more than five hundred hours of operating time on the Pulselight system and the two taxi light bulbs. I had to replace one of the stock taxi light bulbs (# 4509) prior to the Pulselight installation. Concurrent with the Pulselight installation, back around 1992, I installed #4464 bulbs in the taxi light positions. Despite at least five hundred hours on those bulbs, including constant-on during landing and taxi (along with the pulse operation) I have never had to replace one. Note that the factory rated bulb life on both the 4313 and 4509 bulb is only 25 hours.
The two 4464s combined provide as much useful landing light as the single 4313, while drawing less than half the current, and are also fine for ground taxi operations. Sometimes I land using the single 4313, but I actually prefer the more spread out light pattern of the two 4464s. I installed the 4464s as a minor change, as they were in the optional taxi light positions. I retain the high-wattage 4409 as the “official” landing light bulb.
1. You mentioned that the bulbs that are burning out are in the same compartment. That should mean that they are in the left wing. Is there also a taxi light bulb in the right wing? It would be interesting to know whether bulbs also burn out prematurely in the right wing, if you have one there.
2. What are the bulb numbers you are actually using, in each of the positions?
3. If the bulb has a marking on it that says “Top”, it has to be installed in that orientation. If it is not, either the bulb’s light pattern will be incorrect, or the filament support will be incorrect, or both (depending on the bulb). If the bulb is mis-installed and the filament does not have correct support, it will burn out prematurely.
4. The bulb needs the proper mounting (correct notches for the bulb), and the correct retainer. Otherwise the vibration may have an exaggerated effect, or the filament won’t be properly oriented to its supports inside the bulb. Some folks apparently have successfully used things like electrical tape or silicone caulk to cushion the bulb. I would be hesitant to do this if you only have a single bulb, and it is the 250 watt unit, due to the heat. My only other comment is that it should not be necessary. If it helps, it is almost certainly covering up some other problem, either an operational or mechanical issue.
5. Vibration will kill bulbs, while they are on. If you can see your wingtips shaking, during start-up and shut-down, or during cruise, or during taxi, it is hard on your bulbs. Anything that reduces the vibration will extend the bulb life (and the life of many other components).
6. Some of this is under your operational control. Don’t start or shut down the engine with the lights on. Don’t taxi with them on, unless it is after dark. Many people operate with the lights on in the pattern; but they seldom turn them off when they can. In daylight they can be turned off on short final, and can remain off during taxi.
7. Some of this is under maintenance control. Make sure that wiring connections are good at the bulb. Make sure that the bulb is correctly installed. Make sure that the prop has proper balance. A freshly overhauled prop probably won’t benefit much from a dynamic balance, but one that has been dressed annually for five years probably will. Make sure that both the prop and its spinner are installed with correct indexing (good write-up on this in BAC, and past posts on the MML that are very easily searched on BAC). Make sure that the engine mount’s rubber cushions (“Lord mounts”) are in good condition. If the cushions do not properly support the engine, the cushions will bottom out internally against the spacers, putting shock loads into the engine mount and airframe. This is most apparent during start-up and shut-down. Other parts of the engine may also contact fixed structure (like the engine mount) if support is inadequate. For example, the Airborne suction elbow on the Airborne 211CC vacuum pump, on the IO360 as installed in the Sierra, very often has peen marks on it from the engine mount tube just above it. I have often found moving engine parts that have been tied off to stationary parts, with inadequate allowance for “slack” in the connection. That obviates the value of the mount cushions, and transfers vibration directly to the airframe. The landing gear cushion pads (“donuts”) get flat and hard with age. There is a dramatic difference in taxi “feel” between new and old cushions. This is most apparent when the tires are aired up to full pressure.
If you run down all these aspects, and correct any problems, you should not have any problems with bulb life on our planes. You may also be preventing other problems, depending on what you find. Here is an abbreviated bulb chart that outlines some data on bulbs that have the same PAR 36 form-factor. The voltages shown are the intended-rated voltages at the bulb, while it is operating, after the usual voltage losses have occurred in the wiring and connections. 14.2V on a main buss won’t be 14.2V at the 250W landing light bulb when it is on. Some of these bulbs can be hard to find; only specialty suppliers are likely to have them, but most are not particularly expensive. There have been many new bulbs newly introduced to the market in the past 5-10 years, having the same PAR36 form factor. These include quartz versions in which the bulb number is preceded by a “Q”. A semi-spot or spot light pattern is usually OK for landing, as it gives good range along with a sufficiently large lighted area near touchdown. If possible, taxi bulbs should be flood-type rather than spot-type. As an example of misapplication, Beech specified the #4509 and #4595 bulbs for taxi light service, but they are both a very narrow spot beam style. That’s OK when it is being used as a lower-powered landing light, but not very good for a taxi light application.
All lamps are 4.5″ diameter, PAR36 form-factor
4313 250W/13.0V/025hour/140Kcp landing semi-flood light bulb, most commonly specified as a primary landing light. Short service life if left on for long periods, especially during ground operations.
4411 and 4416 30W/12.8V/300hour/035Kcp very low-power taxi light bulb, but good bulb life. Might be strong enough for emergency landing use, with both of them on, but primarily useful for a wider taxi beam. The 4411 is a readily available PAR36 tractor bulb having a faceted lens rather than a clear lens, and produces a nice trapezoidal beam shape.
4461 and 4464 60W/12.8V/300hour/050Kcp taxi flood light bulb (good bulb life; good service and good light dispersion as taxi lights; too weak as a single landing light, good in pairs).
4509 100W/13.0V/025hour/110Kcp taxi very narrow-spot light bulb, most commonly specified as a taxi light for aircraft having two or more lamps. Marginal single-light output for landing light service. Poor light dispersion for taxi light use, and poor bulb life in almost all applications.
Q4509 100W/13.0V/100 hour/140Kcp Quartz landing semi-spot light bulb. Intended as a taxi light, but has been getting used as a lower-wattage landing light.
4519 100W/13.0V/25hour/030Kcp taxi flood light bulb (hard to find but inexpensive marine bulb). Strange mix of low candlepower but short life; specs may be inaccurate.
4595 100W/13.0V/300hour/060Kcp very narrow spot taxi light bulb, but with a much longer design service life than the 4509.
4604 50W/12.8V/100hour/040Kcp taxi flood light bulb (sometimes hard to find but inexpensive)
Q4631 250W/13.0V/500hour/80Kcp landing light bulb (costly new Quartz long-life flood bulb)
Q4632 250W/13.0V/500hour/75Kcp landing light bulb (costly new Quartz long-life flood bulb)
4587 250W/28V/025hour/40Kcp long-life wide-flood taxi light bulb.
Q4587 250W/28V/250hour/40Kcp Quartz flood taxi light bulb.
4591 100W/28V/25hour/90Kcp very narrow spot taxi light bulb.
Q4591 100W/28V/250hour/90Kcp Quartz flood taxi light bulb.
4594 100W/28V/300hour/70Kcp very narrow spot taxi light bulb.
4595 100W/28V/300hour/60Kcp semi-spot taxi light bulb.
4596 250W/28V/025hour/150Kcp narrow spot landing light bulb.
Q4596 250W/28V/250hour/150Kcp Quartz semi-spot landing light bulb.
4626 150W/28V/300hour/025Kcp taxi flood light bulb.
HID lamps are now available. These bulbs can’t literally ‘burn out’, as they have no filaments; they are more like the Mercury-vapor and high-pressure Sodium lamps commonly seen in large-area outdoor lighting. They are also quite expensive. I don’t know of anyone who has installed one in an Aero Center aircraft (so far). If you are considering one due to frequent bulb burnout, there are probably far less expensive solutions. If you have the single landing light, and just want more light, it could be much less expensive to just install the LH and RH taxi lights. No approvals needed for those; just a log entry. It was a factory option, and is a ‘minor change’. That also gives you some back-up for your lighting; something no single-lamp installation can do.