The FAA requires Erickson’s MD-87’s to drop retardant with landing gear down

It is specified in their Supplemental Type Certificate.

There have been several questions and comments from the readers on this website about why Erickson Aero Tanker’s MD-87 air tankers drop retardant with the landing gear down. The most commonly accepted explanation was to reduce airspeed, especially when making a downhill drop. This was why some older air tankers, like the DC-7 according to “Johnny”, kept the gear down.

But Erickson’s MD-87’s are required by the FAA to lower the gear while dropping — in fact it is specified in their Supplemental Type Certificate (STC) issued by the FAA. The reason is the prevention of stalling.

Beaver Fire, MD-87, T-103, South Dakota,
An MD-87, probably Tanker 103, drops on the Beaver Fire west of Wind Cave National Park September 13, 2017. Photo by Herb Ryan used with permission.

Earlier this year Ericson petitioned the FAA for an exemption from this requirement, and requested a “Flaps 40/Landing Gear Up” configuration while dropping, but on June 28, 2017 that exemption was denied.

Below is an excerpt from the decision which was signed by Michael Kaszycki of the FAA’s Aircraft Certification Service:

I deny Erickson Aero Tanker, LLC’s, petition for an exemption from 14 CFR 25.201(b)(1), that would have allowed aerial firefighting retardant drops in a configuration that does not fully meet the stall characteristics requirements on the modified DC-9-87 (MD-87) airplanes.

14 thoughts on “The FAA requires Erickson’s MD-87’s to drop retardant with landing gear down”

  1. Interesting. It’s not intuitively obvious to me how having gear down lowers stall speed. Can anyone explain, if it does?

    I can see how it can provide more margin close to stall speeds (ex. raise gear to quickly increase airspeed, carry more engine power at lower speeds). Maybe that’s what the examining is talking about.

    1. It probably isn’t to lower stall speeds or “prevent stalling.” It’s to make sure the airplane response isn’t too bad if you were to get into a stall. It sounds like the airplane characteristics gear up at Flaps 40 aren’t certifiable (so it has excessive pitch up, roll off, or both!). With the gear down the characteristics are better and thus certifiable — so you need to have the gear down any time you are at Flaps 40.

  2. Much more likely the necessary certification testing was never done F40 gear UP (why would it be?). Whilst the characteristics are very possibly fine, there’s no way of proving that without re-running the tests in that configuration.

  3. SO, basically the aircraft is certified under less then operational capabilities of the aircraft allowing it to fly the mission. Not sure what power settings there using going into the drop, but average spool up time is about 5 seconds. If the MD87 stalls at the altitude of the picture above sorry, but it’s not going to recover. It’s a matter of time and they’ll blame the crew, not good. When does common sense out weigh $$$? It’s just an opinion.

  4. Here’s the bottom line:

    Here’s the key part provided by Erickson:
    “The EAT MD-87 as modified with an external tank , exhibits unfavorable stall characteristics in the “Flaps 40/ Landing Gear Up configuration.”

    The FAA answer is pretty straightforward:
    “The petitioner proposes no additional design mitigations to enhance safety and aid the pilots such as low speed alerting prior to the stick shaker stall warning . Airspeed call outs are not adequate. Pilot call outs can easily be missed due to other distractions in a high workload environment, such as aerial firefighting. Furthermore, training requirements do not propose additional means for maintaining operational airspeeds.”

    My question would be, why didn’t Erickson install an AOA indicator to provide real time stall margin indications and then request a waiver?

  5. These larger tankers have to bleed off a lot of airspeed to approach the drop point and maintain the drop target, visually. Tankers are already operating outside of their intended design when VFR and slipping to lose altitude. With gear down , and increased drag, losing airspeed is easier. On final, with gear down, the engines are spooled a bit more meaning that they might need less time to spool up in a go-around situation. Also, raising the gear in during a go-around will lessen the drag and increase the aircraft’s ability to climb. Maintaining the original approach configuration maintains the existing Vref approach speeds and known performance characteristics, particularly on final and go-around. It sounds like new performance data was needed for gear up-flaps-40 final-approaches, and new procedures or systems were recommended as well. Maybe the situation that the Feds have avoided is a gear up approach where the engines are rolled [further] back to bleed off airspeed, then go-around, but the engines are slower to spool and the gear can’t be raised to immediately improve climb performance, then CFIT. I’ve worked as a flight test engineer on two type certifications. The performance tables in the AFM require hundreds of approaches in each flap setting, gear configuration, CG and weight, not to mention hot weather and cold weather. It’s not advisable to simply do final approaches with gear up without collecting all that data.

  6. What is “a lot of airspeed” ?
    10-15 knots? That is normal. We don’t operate outside the design of the aircraft because we are VMC operating VFR nor do most pilots slip the machine as common practice.
    Don’t guess, ask.

    1. I have watched hundreds of VLAT approaches. I’m familiar with the operations. Operating VMC and/or VFR doesn’t change certified performance data. The aircraft was designed to do 3 degree approaches over an improved airfield. Typical operation is an instrument final with miles of straight glidepath, providing time and distance to trim out. That is not a typical VLAT drop approach.

      There are no perf charts in the AFM for slipping or doing steeper approaches with full flaps, no gear, over unimproved terrain, with the added drag of a drop tank. Combine that with turning the EGPWS off, the demands of visual target acquisition, and fire-induced windshear, I am amazed the feds permit some of these operations. CFIT is a problem and the feds are likely taking a reasonable precautions by pumping the brakes on yet another abnormal approach configuration (full flaps, no gear).

      To do it right, the MD-87’s likely need a flight test program to get new perf tables, which may dictate modification of the stall warning system (which is a big deal). Per § 21.101, that is a significant modification.

      I have proposed a system that provides IFR guidance and CFIT prevention which would make the feds happy and make these type of operations safer:

  7. Dropping at near stall speeds and at a low altitude is just one reason why these pilots large tanker pilots are amazing! The MAFFS pilots fly under similar conditions. This is just one of the reasons why we developed the Guardian Aerial Fire Fighting system. The cargo planes, most often C-130s and C-27Js, make their drops at max CDS speeds and at or above 500AGL. We hope these speeds and heights will provide these crews greater margins if needed. We’re just thrilled to be part of the solution!

    1. Neat. It would be interesting to see your grid test data. The situation at hand with VLATS is that aircraft do fly low and slow. Some are operating with a lot of weight margin and some are with little. Based on people I’ve consulted with, drops at 250′ AG are normal. Long, straight, shallow approaches are not the norm.

      If the proper systems were put in place and the right safety margins restored, there’s no reason why IFR night operations couldn’t be performed. Then tankers could actually put fires when they are cool out instead of just building lines.

      1. Do you have an Airman Certificate issued from the FAA? Have you been PIC during a night precision approach to mins in actual IMC conditions? Are you currently or have ever been PIC type-rated in the AT-802, S-2T, BAe-146, RJ-85, MD-87, CL-415, DC-10, B747, DC-7, C-130 or any past aircraft operated as an air tanker under Part 137? If any of those questions illicit a response that is anything other then a resounding yes, then I think we should shelve the night IFR tanker op folly for a while. And bleed off a lot of airspeed? Slip a transport category jet down a canyon in afternoon turbulence for glideslope correction? It’s called Pitch Attitude+Power=Performance……Day 1 of your private pilot. And most properly engineered “drop tanks” increase performance, not reduce it. The DC-7’s with the “new” A.U. tank design got the same speed at reduced power settings when they were installed, compared to the older tanks.

Leave a Reply

Your email address will not be published. Required fields are marked *