Propeller Overspeed

[Wanderin_dave]

Maybe this should be in a techies forum, but i'll put it here as this is my part of the world. Feel free to move.

Having just read a couple of accounts of uncontrollable prop overspeeds leading to the loss of big piston aircraft. I've got a couple of questions.

Is it something that has been designed out of more modern aircraft? The accounts i read are all pre 1970. I'm only familiar with light twins where a loss of oil pressure will only lead to the prop feathering, but on larger reduction geared wobbily prop aircraft (turbine included) is it something that is still a consideration?

I've never heard of it happening on a single, though i assume a loss of oil pressure to the govenor would lead to the condition. Which you'd think would happen enough for stories to get around.

[Erebus]

An example of what can happen, in this case a Lockheed Electra, N1968R.

08JUN83 En route Anchorage to Cold Bay, the crew noticed an unusual vibration while climbing from FL190 to FL250. The flight engineer went aft to inspect the engines and propellers but noted nothing unusual. A flight attendant went forward to report to the captain that nothing unusual had been observed, when the vibration increased in intensity. As the flight attendant left the flight deck, she looked out the right hand window and saw the number 4 propeller separate, striking the fuselage. This caused a rapid decompression which resulted in a partial collapse of the cabin floor, jamming some control cables. The crew began an emergency descent but found that control was difficult and that they could not reduce power from cruise setting. The autopilot provided minimal control while lowering and retracting the undercarriage with the number 2 engine shut down enabled the crew to descend and climb. Despite these difficulties, which initially indicated a ditching, the crew managed to return to Anchorage. On their second approach, the aircraft touched down nosewheel first at high speed and the crew shut down the remaining two engines which deprived them of hydraulic braking and nosewheel steering. The aircraft departed the runway at slow speed, partially entering a ditch. The aircraft remained on its undercarriage and further damage was limited to that caused by main gear brake fires which were extinguished by the fire services before spreading. The reason for the propeller separation could not be determined as the propeller had fallen into the ocean.
[Extracted from NTSB Report DCA83AA029]

The aircraft was subsequently repaired and returned to service.

[king oath]

A few years ago an RAAF Orion finished up in a lagoon at Cocos Island after a beat up went wrong.

My memory is a little hazy here, but it may have been related to a propellor problemo. A crew member was killed by a hunk of prop if I remember right.

Does anyone else remember more detail about this? I remember climbing over the wreckage on the beach at Cocos where it finished up stripped of equipment. It may still be there for all I know. Nice home for seagulls.

Help anyone ?????

[chimbu warrior]

It hasn't happened to me, but I am aware of at least one case of it occurring in a C-182. The drill is close the throttle and reduce speed as much as possible; it may be necessary to come back almost to the stall. If that dosen't work, shut the engine down. During all this you should be looking for somewhere to land, 'cos that's what you'll be doing next.

[Rhodes13]

Dave mate...

Sorry to hijack but give me a yell when you can... ill fill you in on all the gossip on england

Regards

Rhodes

[sailing]

Wasn't this a problem with the Stratocruiser? I recall a story of a flight from or to Hawaii?? When one ran away and the pilot tried to stop it by cutting the oil supply to the engine. I think it seized (what the pilot wanted) but the sudden stop caused the prop to separate and it took out the other engine on that side.:eek: Eventually got it down somewhere after a major drama. Was it in one of Mac Job's books?

[ruprecht]

king oath.

The Cocos accident was a combination of high speed, heavy weight and g that caused several leading edge sections to separate. In the attempt to get back to the field they ditched into the lagoon with lots of power on the engines (I assume it was max). The props all departed on impact with the water and the #2 prop struck the fuselage, killing the crew member seated in the racks and narrowly missing the TACCO. :(

Incidentally the TACCO in question was one of the FLTCDR's at 292 when I went through there. He took ditching drills very seriously.

ruprecht.

[Wanderin_dave]

Thanks everyone for the replies. What about with modern turboprops? DASH-8, SAABs and the like, is it a consideration?

Sailing, there were a couple of cases between Hawaii and the US west coast involving Stratocruisers, one resulting in the loss of the aircraft. Both make for incredible reading. The accident which got me thinking though was a C-54 that crashed after take off from Miami. Yep in Mac Job's Vol 4.

Rhodes, there's an email in your account mate.

[Led Zep]

Wasn't this a problem with the Stratocruiser? I recall a story of a flight from or to Hawaii?? When one ran away and the pilot tried to stop it by cutting the oil supply to the engine. I think it seized (what the pilot wanted) but the sudden stop caused the prop to separate and it took out the other engine on that side.:eek: Eventually got it down somewhere after a major drama. Was it in one of Mac Job's books?

Sailing, I believe the aircraft in question had an engine failure due to a rupture somewhere in the oil system. Pilots tried to feather the prop but they had lost too much oil so it just windmilled until it seized, snapping the prop off which took out another engine and a chunk of the fuselage. I've got Macca's the book somewhere, but I know they put it down safely in that case. :ok:

[king oath]

Ruprecht

Thanks for the info buddy. I 'd forgotten the details but remember the tragic loss of life.
Regards.

[Richo]

It still can happen.

Most modern turbo prop aircraft have both a secondary prop governor, and procedure to deal with the problem.

The normal governor is of a CSU type which is both adjustable by the flight crew and will govern the prop within a set range. It controlls prop pitch as its primary method of speed control usually using the old flyweight Vs spring and oil pressure method. There are many types of this governer but all basicaly work the same and are suseptable to the same failures in the mech. and oil systems.

The backup or secondary governer is usually a "Fuel Topping" type. Ie, if it detects a prop overspeed past a set range (usually slightly more than the normal governer range) it will start mechanicaly limiting fuel to the engine. This causes the RPM to reduce as the engine is effectivly bieng reduced in power output. These governers are usually ground adjustable only Ie by the ginger beers.

Some manafactures include procedures in the aircraft flight manuals for dealing with such occurences.
The EMB120 Brasilia has such a procedure as a "Phase One Drill". It basicaly involves power reduction, prop feathering and aircraft speed reduction.

A EMB120 was lost in the USA a number of years ago, due to a prop runaway. The details can be found by going to the Embrear web site and looking at the EMB120 accident invesigations or from NTSB site.

[IMC007]

I've recently done the Dash 8 Q400 course and the prop Overspeed is controlled in two ways. Firstly there is the Over Speed Govenor (OSG)which is the 1st propeller overspeed protection and this will kick in when prop rpm reaches 1060 (Max normal rpm being 1020 on the Q400). The 2nd protection is FADEC which kicks in if rpm continues to rise and gets to 1120 rpm, the crew are then alerted.

QRH for Prop overspeed states that affected engine power lever should be retarded towards flight idle and airspeed reduced in an attempt to control prop rpm. If this does not work the affected engine must be shut down ONLY if the prop can be feathered, if prop cannot be feathered the engine MUST NOT BE SHUT DOWN.

[Wanderin_dave]

Thanks Richo and IMC007, great posts. Exactly what i was after.

[Lodown]

I remember years ago speaking with a guy who flew P-51s. At the time, he'd just given one to the engineers as a result of engine overspeed. Apparently, a bunt forward on a knife edge deprives the governor of oil and the red line was exceeded.

[Milt]

P-51 overspeed.

Difficult to come up with a situation in a P/F-51 where there would be oil pressure loss to the CSU/Prop. Used to fly some demos inverted for long enough for the hydraulics to raise the gear into the down position without loss of engine/prop oil pressure. Lots of black oil always came out of the engine breather near the tail when inverted and made a terrible mess back there.

All of the props in that era were controlled out of fine pitch by the CSU with the control in the cockpit only setting the desired RPM yet continued to be called a pitch control. Thus all such props must be at full fine pitch on the ground until the set RPM was reached. I do a double take when I see a museum aircraft with props at other than full fine.

What aircraft had props which would run away to full course or even lock up?

[Lodown]

Don't know the intimate details Milt, just repeating the information as I understood it at the time. The guy was giving some training to another chap in a two seater. Supposedly the trainee put the aircraft on its wingtip and pushed forward. PIC knew about the situation but couldn't react fast enough to prevent the engine going over the red line. As I was told, it was a region of flight (on the wingtip followed by negative g) in the P-51 that was known about and avoided by the owner/PIC.

[barit1]

Here are two that I studied during my Masters coursework:

Convair 580 (http://www.ntsb.gov/ntsb/brief.asp?ev_id=21426&key=0) and Embraer Brasilia (http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001212X16773&key=1)

In the first, the pitch actuating mechanism failed due to heavy wear. Although a special oil analysis inspection was in place to detect the wear, it failed to do so. The failure occurred during high IAS, leading to very rapid overspeed and blade failure, cutting the fuselage in two.

In the second, the pitch feedback leadscrew failed due to wear. A preflight runup check failed to detect the incipient failure. The failure occurred during approach, causing high yawing moment and wing airflow disruption on one side, with uncontrollable roll.

Interesting speculation: IF the Brasilia failure had occurred at high IAS, the overspeed might have caused the prop blades to fail, but their lightweight composite design might have prevented them from penetrating the fuselage, which had occurred in the CV580 accident.