View Full Version : Icing droplet size & a/c certification

1st Nov 2007, 12:03
"The ATR, Q400 and other transport category a/c are certified to fly in iceing with a dropplet size of 50 microns."

Wonder how the pilot can tell what size the supercooled drizzle drops are?

1st Nov 2007, 12:51
The same way one decides whether that bird about to be injested weights <4 LBS (I stand to be corrected on the certification requirements).

1st Nov 2007, 12:55
Indeed talent,

I have personal experience of flying the Q4 through conditions where 51 micron droplets were present and suffered no handling problems (other than the normal ones). This was of course inadvertent, had I been paying sufficient attention I'd have asked for a heading change (yes I ASR'd it).

1st Nov 2007, 13:10
That is the point exactly! Even ATR pilots can't mesure the size of dropplets!
It was not a ATR problem, but a weather problem. Other a/c in the same situation could have suffered the same fate.

American Eagle pilots got extensive training in identifying ice problem areas in the aftermath of this accident. Bytheway; the ATR has a excellent ice detection system onboard. In addition the boots are extended farther back on the wingcord as a result of the accident.

I bet new modifications has and will be done to the new generation Q400. Look at the B737. It would have been dead decades ago if it had'n been for the modifications.

1st Nov 2007, 16:13
Did you know that the Q400 and the ATR and the Airbus A 380 are all certified on the same icing standard, Appendix C, which was drawn up in the 1950s, based on research conducted in 1948. The NTSB has been clamouring since Roselawn to have it revised and brought up to date but, apart from commissioning loads of research from NASA, the FAA has really done very little on the issue. Since Appendix C was written the body of knowledge on icing has expanded exponentially but very litle of it is finding its way into certification. All turboprops, despite enlarged leading edge boots, or heating, are still very vulnerable.

Be careful out there ...

Mad (Flt) Scientist
1st Nov 2007, 21:05
FAA has really done very little on the issue

That's really not very fair, to be honest.

For example, Amendment 121 to FAR 25 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFinalRule.nsf/0/82A6FA43D74E5596862573310069D349?OpenDocument) is a pretty comprehensive rewrite of much of the relevant parts of FAR25, and the result of a long and involved consultation process. (And involving not just FAA but other authorities too; these kind of new rules have to be harmonised...)

The so-called "Appendix X" to account for SLD is still in development, it is true; but while a lot of research has indeed been done, it's nowhere near clear that there's a full understanding of the phenomenom or how to address it practically.

As to the original question
Wonder how the pilot can tell what size the supercooled drizzle drops are?

You can't tell how large they are, but there can be indications to the crew that you're in conditions outside the approved icing envelope. For example, due to their greater size the SLD drops impinge on different parts of the airframe to "normal ice"; observation of an unusual ice pattern may be indicative of "extreme/unapproved" conditions and the cue to get the Hell out of it....

Shore Guy
2nd Nov 2007, 04:22
While on the subject of icing.....

2nd Nov 2007, 08:56
Mad (flt) Scientist said that I was being unfair to the FAA on their actions over icing. So why, one wonders, on the NTSB's 10 Most Wanted Safety Improvements (current version http://www.ntsb.gov/Recs/brochures/MostWanted_2007_09.pdf) does the following action it wants from the FAA top the aviation section:

Reduce Dangers to Aircraft Flying in Icing Conditions
Use current research on freezing rain and large water droplets to revise the way aircraft are designed and approved for flight in icing conditions.
Conduct additional research with NASA to identify realistic ice accumulation and incorporate new information into aircraft certification and pilot training requirements.

The NTSB Board meets shortly to revise this list. Wonder if icing will remain up there.

Mad (Flt) Scientist
2nd Nov 2007, 17:20
There's a substantial difference between "FAA (and other authorities and industry) have done very little" and "FAA (and other authorities and industry) haven't done enough to satisfy the NTSB", since the NTSB often set the bar ridiculously (or intentionally) high".

For example, one of their wish list is "Stop runway incursions....". Perfect prevention isn't going to happen in any real world, so the FAA will NEVER meet that requirement.

8th Nov 2007, 12:19
Mad Flt Scientist wrote:
There's a substantial difference between "FAA (and other authorities and industry) have done very little" and "FAA (and other authorities and industry) haven't done enough to satisfy the NTSB", since the NTSB often set the bar ridiculously (or intentionally) high".

I stand corrected on the proposed icing rule (and they have just published a new wiring inspection rule) but the fact remains that these rules will have little impact on the majority of aircraft flying today. The wiring rule will take more than 3 years to take effect (it's now 11 years since TWA 800). The proposed icing rule will mostly impact only on new designs and the majority of aircraft flying for the next 20 years or more will have been certified according to research conducted in the late 1940s before anyone knew anything about large supercooled drizzle drops.

I wonder if an article published in New Scientist a few years back after Marion Blakely took over is as true now about the relationship between the FAA and NTSB as it was then:

Pray for a soft landing
07 December 2002
From New Scientist Print Edition. Subscribe and get 4 free issues.
Gerry Byrne


MARION BLAKEY may become the first chief of the Federal Aviation Administration to have to reply to official letters she wrote herself. In less than a year in her previous job as chair of the National Transportation Safety Board, which investigates air crashes, she sent 74 major suggestions for making air travel safer to the head of the FAA, which regulates US aviation. By the time Blakey left the NTSB in September to head up the FAA, not one of the 74 items had been implemented, although some are presumably moving through the FAA's labyrinthine pipeline.

Will air travel become safer as a result of Blakey's appointment? Let's hope so. The FAA alone has the power to make safety rules, and it eventually heeds more than 80 per cent of the NTSB's suggestions, albeit frequently years later. This is not to say that it does not often act, sometimes admirably so, on its own initiative. But many lives could be saved if it adopted even more of these recommendations and faster.

For years there has been considerable tension between the two bodies. The NTSB has often blamed the FAA for contributing to fatal accidents. For example, last month a leaked NTSB report stated that the FAA contributed to the crash of an Alaska Air MD-80 off the coast of California in January 2000 in which 88 people died. A tail part had failed due to poor lubrication; earlier the FAA had allowed Alaska Air to reduce the frequency with which it serviced the component.

Similarly, an NTSB report implicated the FAA in the crash of a Korean Air Boeing 747 on the American Pacific territory of Guam in 1997, which killed 228 people. The NTSB found that pilot error was the main cause, but said the FAA had contributed because it had poorly managed, and even downgraded, essential navigation aids at Guam airport. The NTSB also blamed the FAA for contributing to two fatal crashes caused by icing in 1994 and 1997, by failing to update anti-icing standards for 40 years.

For its part, the FAA often resists NTSB safety recommendations on the grounds that they impose unnecessary costs on airlines or manufacturers or even passengers. Yes, we can make airliners safer, runs a popular FAA mantra, but that will mean ordinary folk won't be able to afford a ticket.

The FAA is often accused of having too cosy a relationship with the industry it governs. For years it lined up with plane makers and airlines to resist a plea by the NTSB to retrofit better black boxes to existing planes to aid crash investigations. And it took until this year to order an overhaul of potentially defective rudder systems on Boeing 737 aircraft that the NTSB had asked for in early 1999. The FAA mounted a media campaign to counter the NTSB's demands, although it later conducted its own research that proved the NTSB correct.

Perhaps the greatest tragedy was the FAA's long-standing refusal to order airlines to put smoke detectors in luggage and cargo holds. In 1996 a ValuJet DC-9 crashed in flames in the Florida Everglades shortly after take-off from Miami, killing everyone aboard. The fire, which started in the cargo hold, may have ignited before the plane became airborne, in which case a smoke detector could have warned the pilot to abort the take-off and evacuate the passengers.

I will take to my grave the pain and bewilderment I saw five years later on the face of Carole Reitz, who lost a son in the ValuJet crash. As far as she was concerned, the FAA's prevarication on smoke detectors was a betrayal. "I thought that government agencies like the FAA were supposed to protect us, not save the airlines money," she told me. The administration later agreed to the installation of the smoke detectors, but allowed airlines several years to do so, and when I met Reitz she was furious that some had still not done so.

Such delays are not unusual. Three items on the NTSB's "most wanted" list have lingered there for years. One, the updating of anti-icing equipment, has been on the agenda since 1981. The others are calls for action to prevent collisions on runways and to protect fuel tanks from explosions.

One of Blakey's aides at the FAA has told me the new chief intends to "pursue" NTSB recommendations. All of us who fly should hope that she does. Most airline regulators around the world wait for the FAA before acting on safety recommendations. A prime reason for this is a complex series of agreements between European governments and the US to harmonise the specifications of passenger aircraft. In most respects these agreements are good for safety, but they also make it difficult for any one European country to order changes unilaterally.

Washington effectively controls the pace of change in international air safety. Given that the FAA has up to now delayed, watered down or even rejected many safety recommendations emanating from the NTSB, Blakey has taken on quite a responsibility. Let's hope that, sitting in a different boardroom, she will not find herself disagreeing with some of her own recommendations.

Gerry Byrne is a science and technology writer living in Dublin. His book, Flight 427: Anatomy of an air disaster, is published by Copernicus Books (2002)
From issue 2372 of New Scientist magazine, 07 December 2002, page 29

9th Nov 2007, 07:45
NTSB yesterday held a board meeting to review its most wanted list of safety items it wants the authorities to deal with. Despite recent pronouncements by the FAA, icing remains on the list as follows:

AIRCRAFT ICING -- The consequences of operating an airplane
in icing conditions without first having thoroughly
demonstrated adequate handling/controllability in those
conditions are sufficiently severe that they warrant a
thorough certification test program. The FAA has not adopted
a systematic and proactive approach to the certification and
operational issues of airplane icing.

Recommendation: Complete efforts to revise icing
certification criteria, testing requirements, and
restrictions on operations in icing conditions. Evaluate
all aircraft certified for flight in icing conditions using
the new criteria and standards.

Timeliness Classification: Unacceptable.

9th Nov 2007, 07:53
The more I read about the behaviour of the atmosphere, the more I realise how little we know about what goes on up there. At high altitudes you can actually get ice crystal "showers" as water vapour condenses directly into ice, not cloud, which then descends under gravity until it reaches warmer layers and evaporates. That's more or less what's happening to the fallstreaks you see on typical mares' tails. And probably causes the sort of icing you described.